btw default rifle is nice, plus it's faster that the M4 but I think it has a bit less spread.
But yes, default rifle is nice, but again, M4 has perks. If you like the shotgun affect of course.
For 15k you should save, or buy some pistols, I suggest dual Desert Eagles, Mk23's, or dual five sevens for spar, which I recommend above all (Tzek is no longer available, but an Mk23 is very simular)