No offense intended but different ports won't help your cause nearly as much as more VOLUME! 2.18 is fine if you are running a Fi BTL 12...but as for a 15 you need about 1ft^3+ more to achieve good output. I would suggest building a new enclosure in excess of 3 cubes and sticking to the slot port. Then add your 45's, glass, etc. You won't regret it. If you pm me your max dimensions I will whip up a design for you. Be sure to tell me how you want it tuned, port location, and woofer direction. Thanks, Justin.