Use external binary morphs. I have saved to my library a V4 with nearly all the morphs (++, Elite, Aiko4, Stephanie4) and it loads in less than 5 seconds in my machine. And I also don't care for the PZ3(Z) scene size file because they directly point to my custom PMD V4 file and I did the same with clothes, hairs and props (even with extracting geometrie datas when needed) so all my scenes size are only around only 500kb and load very quick.