Note the new P2Pool Hardfork version 15 currently does not support the BitcoinXT client (neither the 0.11C nor pre-release 0.11D version) and won't fully startup unless you're running BTCore 0.11.2.
Forest: when BitcoinXT gets the BIP65 pull request merged in, will P2Pool be able to support the resulting BXT version #?
I'm not sure what version number they'll use, but when they release it (and somebody tells me), I will whitelist it and release P2Pool 15.1.