Question about P15 engine

My Discovery 2 TD5 is fitted with a P15 engine, but camshaft and rocker shaft are from a P10 engine, does this gives big difference on engine torque or any work than P15 camshaft and rocker shaft?

I know there is a difference between P15 and P10 engines but I'm not sure, will it make any difference if P15 engine will be equipped with camshaft and rocker shaft from P10 engine, I just trying to find out why my D2 td5 have such lazy start and can't climb up on steep slopes without Low gear.
On higher speed and with turbo it's ok, drives well but a start is horrible.
I replaced MAF sensor, cleaned all rest of sensors, blanked EGR, planning to replace Waste Gate Actuator for Turbo and Fuel Injector Wiring Harness Engine Loom I don't know what else to do please advise anyone