It's a great sub for what it does, but if you put it up against nearly any ported 15" model from an ID sub maker, you might come away disappointed. That said, it's still not a bad sub, and you're on the right track; don't automatically assume 15" means more performance over any 12; it's not that simple.
It's good you're doing your research and know pretty much what you're looking for. For my money the SVS PC12 Plus is a fantastic sub if you can get away with the WAF.
Good luck with your purchase.