http://www.gasgasrider.org/forum/showthread.php?t=18988
The 15 fork is plush from the factory, but has a mid valve spike due to excessive float, with a stiff mid valve - good for elite riders.
If you want somewhere to start tuning look at removing the mid valve bleed shim, reducing the float to .3 or .4 and softening the mid valve stack. You can leave the base valve for a good improvement (initially).
Make sure the pfp is less than 2 turns in from all the way OUT. A good way make sure of its setting is to wind it lefty loosely till it GENTLY seats and then wind it righty tighty 1 turn then see how the fork performs then. If you've got more than 3 turns set it can get uncomfortable.
Ps you get the best out of this bike with correct springs for your weight/speed.