is the same happening with your stock motor? Or just with firebolt? Don't really remember how was with that esc (i used it long time ago) but firebolt is not very powerful so should be no problem. Your esc should work with min 15t, but things happenes. First check esc with stock motor witch is if my memory is good 21t or 28t.
anyway for drifting 15t firebolt is not great, you should use motor with more t and more powefull.