For anyone looking to play this game, for the love of god, ignore the hours outlined in the roadmap. I don't know if the creator comes from another dimension where the hours are longer or what, but I have done everything in the game in the most efficient way (won every race first go etc, boosted online) and I am way over 15-25 hours. I would go as far to say it is literally impossible to complete in 15 hours, 25 hours probably too. On Steam, my hour count is currently at 45 and I still need to grind out 7 more levels online!
So, to sum up, I thought I was in for a cruisy 15-25 hours, but in reality it is more like a 50 hour slog.
Done with achievements.
I apologise for any incomplete achievement guides.