15p is obviously the later model, and featured several improvements to overcome some of the problems encountered in the 10p model.
I'm no expert, but from what I have read most of the changes were in the head, as injectors are different...metal dowels replaced nylon ones...egr set up changed... fuel cooler changed...fuel pressure regulator changed.
Shifty is your man on this subject... he has far more TD5 experience than most on here.
I run a 10p, and at 112,000 miles still going strong.... touch wood!