Is your library still embedded or free floating via your general preferences.  For me, DSON imports slows down with an embedded Library.

Set your DSON subdivision to zero once a figure is imported.  This is also a point of slow Poser response.  This is no reason to have subdivisions active when composing a scene; have Poser do the subdividing during render where it counts.

Yep, the more morphs you load into Genesis/Genesis 2, the larger the model file becomes.  ATM, the only work around for this problem is move each DAZ morph type from its current program folder and create cr2 figures in Poser of individual morph sets.  Afterwards, recombine the files.  Unfortunately, with this approach, you will not be able to inject new morphs into established cr2's, you will need to generate a new DSON import.