I had a pz3 that ran 125 mb , compressed it was 22.

morphs are not embedded geometry in the sense that Phil means. Poser props often wind up with the obj file embedded in the pp2 file, and no external obj file. These will benefit from making the obj a seperate file.

SWaving with external binary morphs will reduce the pz3 but then you have extra pmd files to keep track of.

look in the freestuff, poser utilities for geomstripper.

 

It seems to me I did a script recently to save poses from a scene to allow one keyframe to be extracted to a new scene. That may give you a base for what you want.A search of the poser and python forums should find it, maybe wishlist.