The Austrian team lost their place as best of the rest to Ferrari, frequently found themselves outpaced by Williams and managed just three podiums on their way to fourth in the constructors championship.
Their total of 187 points was by far the lowest they have ever achieved under the current scoring system, and 2015 was the first season since 2008 in which they failed to win a single race.
Their car that year was the RB4, and in the hands of David Coulthard and Mark Webber, it scored just 29 points. But 2008 wasn’t a total loss.
The RB4 was also entered by sister team Toro Rosso, painted in different colours and with a different engine in the back; with Sebastian Vettel at the wheel, it won the 2008 Italian Grand Prix.
Thanks to Vettel’s victory, Toro Rosso ended the season sixth in the constructors’ championship with 39 points, beating their big brothers for the first—and thus far, only—time in their short history.
A Ferrari engine powered their success back then, and 2016 will see the relationship with their fellow Italians restored. Toro Rosso will use year-old Ferrari power units, while Red Bull will, as they were in 2008, be users of a current-specification Renault.
Power-unit performance has been the key to on-track success since the start of the V6 turbo hybrid era, and smaller teams have often come out on top against larger rivals thanks to a bit of extra grunt.
The Ferrari engine that raced in the 2015 Abu Dhabi Grand Prix—the specification Toro Rosso will be using—was substantially more powerful and reliable than its Renault counterpart, and there are no guarantees the French manufacturer will make any significant progress over the winter.
So are we about to witness the most shocking giant-killing in recent memory—could Toro Rosso beat Red Bull?
The early races of the 2015 season saw the smaller teams punching above their weight on more than one occasion, and Toro Rosso certainly got off to a flyer. As Red Bull struggled to get to grips with their new RB11, the junior team often came out on top.
The first time they did it was at the Malaysian Grand Prix at Sepang. Though unable to match Daniel Ricciardo and Daniil Kvyat over a single lap, the two Toro Rosso rookies—both on only their second F1 start—got the better of them in the race.
Max Verstappen drove around the outside of Ricciardo at Turn 1 on his way to scoring the first F1 points of his career for seventh, while Carlos Sainz Jr. recovered superbly from 15th on the grid to take eighth.
Kvyat could only manage ninth, and Ricciardo was 10th.
Both Toro Rossos beat both Red Bulls on only one further occasion where all four finished, at the Japanese Grand Prix later in the year, but seeing one of the youngsters come home ahead of a driver from their big brother team was not that uncommon in the first half of the season.
Verstappen was going to be the top driver of the quartet in China before his late car failure, Sainz famously snatched ninth from Kvyat in Spain with a late pass and Ricciardo found himself starting the Austrian Grand Prix behind both of the Baby Bulls.
Sainz didn’t make it to the end in Spielberg, but Verstappen came home in eighth—two places ahead of the top Red Bull.
The strong performances of the junior squad were something of an embarrassment to Red Bull. Since the start of 2014, they’ve been laying the blame for their lack of competitiveness firmly at the door of Renault.
For the most part they were entirely right to do so—the French manufacturer’s weak power unit was indeed the primary reason they were no longer a front-running team. It lacked both power and reliability, putting Mercedes far out of Red Bull’s reach.
But it wasn’t the only reason, and after qualifying for the Spanish Grand Prix—where the Toro Rossos stunningly locked out the third row on the grid, half a second clear of the Red Bulls—Ricciardo admitted his team had problems on the chassis side as well.
But it wasn’t just Red Bull, either.
It wasn’t the case that Toro Rosso were accidentally beating a big team because the big team was having problems—the Faenza squad had built themselves an exceptionally good car that was a match for almost anything else on the grid.
BBC Sport’s Andrew Benson revealed late in the season that engineers down the pit lane considered the STR10 to be one of the top three chassis—better than the Ferrari SF15-T and McLaren MP4-30.
And it had been produced on one of the lowest budgets in F1. Per Autosport’s Dieter Rencken, Toro Rosso’s 2015 budget was just £90 million—equal with Sauber, with only Manor spending less.
By the end of the season, Red Bull had unlocked the secrets of the RB11 and pulled clear, but the Toro Rosso was still a quick, competitive car all the way to the final race.
Technical director James Key is going nowhere, and with the regulations remaining stable for 2016, we can expect the team to do another fine job on the STR11. Matching the RB12 is beyond them, but they can certainly get close.
The STR11’s main weakness will be the power unit. Toro Rosso are using year-old Ferrari engines for 2016, frozen at the specification used by their Italian neighbours at the season-ending 2015 Abu Dhabi Grand Prix.
But for all this is a handicap when it comes to fighting the very best teams, the 2015 Ferrari was a very, very strong engine—and there’s a good chance that, at least for the early races, it will be better than the 2016-spec Renault engine being used by Red Bull.
All the teams have advanced simulation technology, so the second-per-lap figure was not plucked out of thin air—Verstappen will have seen the data, and from that he will know almost exactly what sort of gains the Ferrari will provide.
That full second would, at almost every circuit, have been enough for Toro Rosso to comfortably beat Red Bull in 2015.
But whether it’s enough to put the junior team ahead of the big boys in 2016 is largely down to what Renault can do in response.
Red Bull’s 2016 power units will have “Tag Heuer” written on the side, but under the skin, they will be Renaults. Though the French carmaker’s 2015 engine was poor relative to the Mercedes and Ferrari, it does possess one thing its quicker rivals do not: a lot of room for improvement.
The closer a power unit gets to the theoretical maximum possible performance level, the harder it is to make substantial gains. The Renault is a long way from that optimum, so a gain of a full second, maybe more, from 2015 to 2016 is not an unrealistic target.
It’s not guaranteed—there remains a chance the power unit will remain as far off the pace as it was last year.
But Renault have surely exhausted every possible route to failure, and they can now call on the assistance of engine experts Ilmor—best known for building the Mercedes engines that powered Mika Hakkinen to back-to-back drivers’ titles with McLaren in the late ’90s.
If the new Renault is “close” to the 2016-spec efforts from Mercedes and Ferrari, it would almost certainly give Red Bull enough power to hold off their sister team. Both will create quality chassis, but Red Bull’s budget is far higher and—with respect to Toro Rosso—they have some of the best personnel in the pit lane.
They’ll produce one of the best cars and, once the improved Renault engine is ready, common sense tells us they will be ahead.
But before it’s ready? That could be a different story.
Renault proved in 2015 that they will not rush upgrades until they are satisfied they are ready. The supplier had 12 tokens left over from the pre-2015 winter development phase, but by the time October rolled round and the season was nearly over, they hadn’t spent any of them.
Autosport’s Lawrence Barretto reported they had used 11 tokens before the United States Grand Prix, but the upgrade wasn’t run until the penultimate race of the year.
If Renault drag their heels again in 2016, Red Bull could face a significant wait for a proper boost in power—and this could open the door for Toro Rosso, with their solid, reliable and all-round decent 2015-spec Ferrari engine, to be quicker in the early part of the year.
Finishing the season with more constructors’ championship points than their illustrious stablemates is surely too much to ask.
But it won’t be too surprising if Toro Rosso have their noses ahead when the European leg of the season kicks off in early May.