the 15's may hit harder, but if it was mine i would pick the 10"'s. I would think that 6 10" cvx would be louder than 2 15" cvx's, but u said 10" cvr's. I would still get the 10"'s especially if the 10's were cvx's.
Honestly no one can say, it really all comes down to how much power you will be giving the subs and the install that you give them. How hard a how good a sub hits is like 80% dependant on install.