JBL prx915 vs prx618

Hey mates, I’m wondering if anyone has experience with these woofers and can tell me which are better performance wise and for the buck. I was looking at maybe upgrading my Rockville rbg15s woofers for a pair of JBl’s to match my up tops which are PRX912’s. I noticed there was a pair of each on Facebook marketplace for around 1500 and I just thought I’d see what you mates think about either or.