mori not unresponsive, but quite slow

hello.

I am working with a mori file approximately 12MB of size, maybe 50 text files in it, some of them contain images, and it is so slow that I've started to go back to TextEdit now and use mori only as storage and organizer, but not for working. Typing goes like I type a phrase and then I can watch it appearing on screen like some remote typing is happening. When I try to highlight a few lines and then do a right-clik on that, it sometimes goes allright, sometimes gives me a spinning ball for up to 30 seconds. Same going opt-backspace to delete some words, etc. Quitting and starting it up again sometimes seems to speed it up a little bit, but not really. Is there anything I could do about this, like emptying the cache or something?
(I work with Mori 1.6.9d19 (01060.90.19) and Mori 1.6.8 (01060.89.99) (same problem in both), and a 1.67 GHz PPC G4 with 2G Ram and OSX10.5.2, and other apps, like Adobe InDesign, run relatively smoothly.)

thanks, best

s.