Yes, Your sub could definitely use an upgrade. Your room size (
http://www.audioholics.com/loudspeaker-design/subwoofer-room-size) is close to be Large on that chart, but your sub is (my guess) certified for small rooms.
$1500 could get you decent amount of sub.
How many seating spaces do you care to have good bass at?
1-2 or more like 5-6?
If Prior - you could get by with one good sub, while for latter you pretty much must invest in two.
pb2000 is solid sub - no doubt, but this one will knock the socks out of it:
http://www.hsuresearch.com/products/vtf-3mk5HP.html
If your significant other's don't mind this pair:
http://www.hsuresearch.com/products/vtf-3mk5HPDual.html could do serious internal wall restructure if you let it rip full steam