shouldn't be too high cos the D2 is set to 18.85psi from factory and can be adjusted to 20 from the wastegate rod without any other ad-on, also the higher the boost is the lower the EGT goes... if you have only 15 it's too low so that's the problem...did you clean the MAP sensor, do you still have the EGR? ...that's why without propper diagnostic is hard to give an answer cos if the AAP(airbox) sensor fails the ECU goes to default of max 15psi boost

