1. User IrfanView to reduce all textures to 1200 x 1200 or less.
2. Load only the morphs which you actually use. Combine "dial spun" characters that need several morphs into a single new morph and delete the rest.
3. Use V3RR and M3RR instead of V3 and M3.

Unless you do poster size print-outs of close-up mugshots, none of the above will be noticeable in the final render, but drastically improve Poser's performance.