I currently run a Kicker 15" L7 in a vented box and a Kicker Zx1500.1. I want it louder. I do not want to pay for a more powerful amp, but I would like the loudest sub and box with the given wattage. Am I better off with 2 12" L7's? 2 15's? Give me your recommendations for best SPL on 1500 watts. Must fit in the back of a '10 Explorer.