caveat my response: I've only sampled Velodyne, but use Meridian sub -

But I have a similar size room and have used both 1 and 2 sub configurations; My vote would be in favor of the 2 dd12s; I think the 15s would be too much, given the musical nature of your use pattern. Faster reactive times are more critical... and 2 12s will be more than enough air moving power; I presently use 1 dual driver and can move the room with it when required...!

ken