Well, your subs are pretty good. It’s just that in the world of subwoofers, there are options that can give you better performance. And not necessarily for a lot more than the ones you have. The thing is, ya don’t know what ya don’t know. But once you experience it, it’s hard to go back. I was there too. 25hz JBL subs, and thought Terminator was rockin my house. Then when I got my first big boy sub and Kong shook the couch in a totally different way, I was hooked. My friend owns two car audio stores, and I’ve experienced all kinds of punishing bass. There’s just nothing like real ULF.
Hope you didn’t take anything I said as an attack or anything. I was only trying to give you an idea of things in regards to your question about the 15’s. Unfortunately the answer isn’t nearly as simple as 12 vs 15. I don’t know Canadian pricing, but iirc for 1k each, a pair of PC2k pros would open your eyes! Of course there are other options like
@Pogre ‘s HSU or monolith and Rythmik etc. But don’t know about availability to you.