also, when it says 1500 watts, that's not completely accurate.
it would be if the driver were just a pure resistor at 4 ohms, but in an actual enclosure, the impedance swings up and down depending the port tune and the driver's resonance.
here is the impedance, in a martycube for example:
and the actual power, with a "1500 watts" setting:
the power peaks around the tuning frequency of the sub. is lowest at where the impedance peak is at its highest (which is the resonant frequency of the driver in the cab). and then is limited again on the top end by the low pass filter that most folks would use (in this example, i put a 4th order low pass at 80hz on there, which again, is what most folks use or at least start around).