I have used and sold (I'm a contracting dealer but only serve as a private bassist on this site) quite a few sets and they really do sound great. The subs are very meaty and the top boxes are very smooth.
I will say though, that I find the JBL PRX series to be a much better sounding set of top boxes and the sub in the XLF version is much manlier than the ELX-18P.
But if budget says the ELXP's are the better fit, you will not be disappointed. I'm just saying the JBL's are crisper in the top end (as one expects with JBL) but much more thump from the subs.
I do prefer the smoothness of the ELX-12P over the ELX-15P. I do recommend the 12" with the sub over the 15'.
Keith