Yeah, I wouldn't go for nearly as large and low tuned a setup as Rodny is using, as one of the things I took into consideration for his system was that he would have four drivers on hand. Because of that, I felt it would be best to trade a little headroom from each driver in return for extra deep extension.
For just one 15" driver, I'd be looking at tuning in the ~15hz range to keep a good balance of extension and headroom. The RL-s15 doesn't like ported enclosures, it's made for small sealed car applications. Instead, staying in that price range, you'll want to take a look at dual RL-p15s or a single RL-p18. Let me know which way you want to go
