You saying DD1512 vs Kicker L7 12"???
That is kinda a funny comparison...a 500wrms sub against a 750wrms sub nearly twice its MSRP.
The DD1512 will hold its own, but the L7 will take it. (given the power and box)
BUT, the box can make a HUGE difference. For instance, the other local place here in my town builds 'custom' boxes for L7 12's. My box w/ a DD1512 on 500-600w vs their L712 on 500-600w, and the DD1512 will jump up and surprise you. I have shown that to people in that shop (heads up comparison).