ok, it is not realy significant with pitch 15 deg, but also for the calculation for the pich-up moment for the engins (toga...) you need the different in height between the engins and CG...
Well, there could be some debate here.. its often said you only need to do the sums about a (any) fixed point (usually the c.g) and resolve them all out as a single force vector together with a moment (torque)
However, instantaneously, the engine thrust moment
will rotationally accelerate around the c.g. but in resolved
steady state flight the nett lift and drag centres are where the thrust will be opposed from. So only in accelerated conditions will the c.g. be the obvious force resolution centre.
Agree?