Well I'm probably not the best to lay judgement on this as I'm 54 and my hearing is damaged from years of abuse and work. But for HT, its a no brainer to me, go for the FV15HP for its tremendous output. There is no doubt the sheer output of the FV15 clearly tops the F15, and I have a huge room ~ 7000 cubic feet. And relying on my music memory, I give the nod to the F15. My F15 just disappeared in my room on delicate detailed music. And I listen to much more music than watching movies so.......I'd say if a guy was 70/30 music/HT, I'd go sealed. The only reason I replace my F15 is because it drowned in a flood.
But Brian has stated in his opinion, the differences between the two models are like splitting hairs. And I trust Brian's ears and opinion more than my own. He designed and built the subs. And I'll say it again here for anybody on the fence, Brian is a stand up guy......you will find no better service and attention in the business, imo. You may have to be patient sometimes, its pretty much a one man band assembling and testing, but its worth the brief wait in the end.