A 1515 has too much power to be usable on a track in a buggy. A 1512 will have plenty of power and longer runtime.
If you use an esc like the mamba where you can adjust the settings,it is controllable on the track and there is that extra power when you need it.The 1515 is more efficient than the 1512 for it has more torque
Mike Cronin the owner of this website uses that setting as well
Brushless Jammin Truggy on NEU 1515 2.5 D on Monster mamba max with maxamps 5000mah 6s Lipo
Gorillamaxx Revo CF version on Mamba maxx ESC with NEU 1515 1Y on Maxamps 4s 8000mah Lipo