You need good bass to start with, 15" or 18", the best subs I sell are the FBT or RCF, but they are on the expensive side but are light small and hit hard.

As for your tops. The only reason to have 15" like you have is if you don't want to use subs for smaller rooms or lower volumes.

I personally would spend money on a pair of 15 or 18" subs, then I would get 12" and horns for the tops, crossover the tops so they play around 80hz and up, maybe even a little higher, then set-up your subs with an Aux send, so you send only what you want to the subs, like drums, bass, arranger. then you have everything else go to the tops only, this way you clear up the midrange for a better punchier sound without taxing the speakers, and you add the umph to what needs it.