I have no experience with feather pecking, but from reading a lot, I’ve learned it often starts with boredom and not enough space. Keeping different breeds doesn’t help either.
And if you have this problem its difficult to get the bad habit undone. Providing much more run space with hiding...
14-15% is fine for heritage breeds. Only laying hybrids and high productive breeds that lay an egg almost every day need feed with higher protein levels.