loud is subjective though. personally nto a huge MTX fan but from what ive heard the 8500s and 9500s are loud. so i would imagine that 3 15s would do the trick.
This must be a trick question or something?? Give me (3) 15's and I'll give you broken sternums! Should be extremely loud if done properly. I'd recommend 800-1000 watts per sub.
are u getting an individual amp for each sub? I mean I know "Loud" is a pretty plain term for all the choices there is out there but I would probably just go with a pair to avoid funky final ohm impedance. But if u already know about the ohm impedance thing and u already have an amp ready for 3 subs I gess yea it will be a good setup.