I would probably pick the Kappalite 3015 for a two-way crossed over at 2 kHz. Here's why:
1) A 15" woofer will be beaming somewhat between 1 kHz and 2 kHz, and if it has a rising response in that region, this can be used to partially offset the effects of beaming on the power response. The 3015's curve looks to me like a better starting point in this respect.
2) The 15PR400 has a fairly broad, roughly 3 dB dip at 1 kHz, which probably contributes to its subjective smoothness, but if the goal is "flat", then that dip is a problem. Passive EQ in the crossover can bring down a peak, but it can't bring up a dip. On the other hand, the 3015 doesn't have any significant dips.
3) The 3015 starts rolling off naturally not too far above 2 kHz, while the 15PR400 holds up for another octave or so. This means that a more aggressive (higher parts count, more expensive) crossover will have to be used to roll off the top end of the 15PR400 if the goal is a good transition in the crossover region.
I certainly don't mean to say that the 15PR400 would be a bad choice for a two-way, but imo in this application (2 kHz crossover) the 3015 has a bit more potential.
The box requirements are virtually identical; Fs, Qes, and Qms also come into play.