I run dual XS15s in a room that's 17x11.5x8 with a small opening to the rest of my home. The system where they're installed produces the best bass experience in the house. This is compared to other subs in other rooms, which were both, at one time or another, installed where the XS15s are now.
I'm still learning but I'm pretty sure there's massive low frequency gain in that room, and I know that there's only crude EQ for the sub channel; so a sub like the XS15, with its long, shallow rolloff, matches my room really well. Music is gorgeous; HT is thrilling. Plus I'm never near the output limits of either unit, so there's never any ugliness.
Anyway yeah. What I'm saying is, I'm having the time of my life with dual sealed PSAs in a space rather similar to yours. Fling Tom an email and discuss your goals
Edit--Yes, I have also used a powerful ported sub with a response that's flat down to the upper teens in the same space. In my opinion, the XS15s are better for all content there, although not quite as impactful in the region between about 30Hz and 18Hz. However, this slightly reduced impact doesn't result in an anemic sound; it results in what I can only describe as a more detailed sound. There's a lotta doubters and naysayers when it comes to sealed subs, I think because it really is false that ported subs aren't good for music and don't have strong output at very low frequencies; that they are inherently 'boomy' or whatever. That's certainly all bunk. However it is true, in my opinion, that if you are blessed with a small listening room, then you should take advantage of the way a sealed sub with a traditional, long and extended rolloff interacts with small rooms. Have no fear! Go XS15!