Depends on the 15 turn motor you get.
Are you racing at all? You may want a good stock motor then. The P2k2 pro is a good stock motor. The MVP is also good in Offroad if you do the tricks that Big Jim recommends here: www.bigjimracing.com
The magnets in the MVP last longer.
If no racing, a 19 turn motor would be a good choice as well. You can get the Reedy 19T Quad Mag motor, lots of power and torque there. The Peak Dynasty is a good motor too.
If you go with either of the 19T motors I suggested, start at the recommended gearing for 24 degree motors minus 1 pinion size for the Dynasty. If you have a track to test it on run it so it peaks out in speed towards the end of the longest straight.
The Reedy Quad really likes to be geared up ( bigger pinions ).