I wouldn't recommend running one 1500 to each voice coil. If the amps aren't strappable, then just sell the one you have now and upgrade to a single amp somewhere around 2500-3000W RMS @ 1 ohm and buy the Dual-2 version of the BTL.
If you run two amps, not strapped, to individual voice coils on the same sub, then each coil will be getting different signals. Sure you can split the input signal but it will be almost impossible to get the exact same amount of power running to each coil all the time.