The soundsplinters are excellent subwoofers, and the owner, Mike, has some of the best customer service in the industry. The Rl-p's are essentially sound quality subwoofers with great output potential.
However, a 1501d at 2ohms, even unmodded, would indeed be too much power for a single Rl-p. If you ran that amplifier at 4ohms it would be more the Rl-p's style. 700-800w the Rl-p's shine. 1kw is still relatively safe if you use your head. More than 1k and you're really pushing the limits of the subwoofer, and they probably won't like it too much.
If you are more SPL oriented and want a single sub setup, I'd look into the Eclipse Ti's or the LA Storms, or something that'll take full advantage of the power that amplifier is capable of delivering. If you are more into sound quality while still having great output, then run that amplifier at reduced power to a Rl-p.
Or, if you want to go with a dual sub setup, a pair of Rl-p's would handle that amplifier.