I say try the 15 out, if you dont like it sell it. Like one guy said this is the age old question, cone area vs power/motor force. This is the beauty of the car audio world, there are so many variables that influence the results, car type, enclosure, sub, amp etc. Everyones perception of loud is different. Some guys dont consider you being loud unless you are doing 147+ on the termlab. Others like to hear or feel the bass, and could care less about what it metered. You never know what "you" like untill you try it.