Unless you have your 18 at 2 ohms also, why would you even try to compare the 15 to your 18?i just hooked up a sx 15 off a aq 2200d @ 2ohm (1400 watts or so) sounds pretty good its tuned to around 36HZ 3.4cuft in a trunk vehicle. dont compare to my 18 but it does get down nicely and sounds clean.