Just posted details of a new design for a compact 15" Sub on my web-site. As soon as the plans have been cleaned up I will get them posted on the FSP Forum.
This is the big brother of the Q12 Mini Sub. They both cover the same frequency range however the 15" is approx 5db more sensitive and has the same power handling, however it does require external EQ to meet its spec. being an assisted design similar to a B6 alignment.