Welcome to the Shack,.... yup, there are a few folks around here with 15" subs, and a few with 18" subs, and a few (like me) with dual 12" subs, and some with dual 15" and dual 18" not to mention what some of the guys with IB set-up have done
Before you get too carried away with your new box for the RS sub, check out the DIY Sub forum here at the Shack, you'll get all sorts of useful help and info there.