Even though it is super easy to do, if anyone doesn't want to have to play the game again to get the speedster trophy, here's a trick...
Let your game run past 100 hours. At that point the counter restarts at zero and if you beat the game under 15 hours then it still registers as less than 15. Did this by accident but it works.
Let your game run past 100 hours. At that point the counter restarts at zero and if you beat the game under 15 hours then it still registers as less than 15. Did this by accident but it works.