I'm a brand new member, and just bought the HD15s 15" Precision Acoustics subwoofer from Best Buy for $299 - what a deal for 15".
At the same time, I also bought 2 x 12" Klipsh sub-12 to do a side by side.
Apples and Bananas!
For HT, the large, long port of the Klipsch 12" absolutely shatters the PA 15" dual really short port to oblivion and beyond. If you want a really mammoth LFE power house, just 1 Klipsh 12" is all you'll need. My room is about 20x20, so a relatively good size open living room.
However, for musicallity, the HD15s does sound cleaner. The Klipsch sub-12 is muddy, so turn the low-pass nearly all the way down, and depend on your surround woofers to make up for gap.
Both model made in china, both target the catfish (bottom feeder) market.
So there you have it.
For Purely LFE = Klipsch Sub-12,
Down firing, long and large rear facing port
freq. resp: 24Hz - 120Hz
For More Musicallity = Precision Acoustics HD15s
Front firing, very short dual small-mid size rear facing ports
freq. resp: 35Hz - 150Hz
Both were $299 on boxing week up in Canada at BB.
I'm keeping just the 1 Klipsch, it's got a 5 year warranty, so I'm refunding the BB 9 year extended warranty, as my CC covers an extra year.