After some grinding I managed to beat all 15 stages in less than 14 minutes. The run is not perfect but it taught me a few tricks.

Drifting is needed in a few corners, but it prevents slipstreaming and can do some crazy physics.

I first started with the cars that have their top speed maxed out, but this proved to be a problem in the last couple of stages (and of course, Coniferous Forest) So I went for the cars that handle a little better.