WP 3.0 Menu – big Save Menu problem

I have transferred about 100 pages into WP, successfully, and I have (re-)created the site navigation using WP’s own simple drag and drop method. About 6 main headings with child pages, one heading with 6 subs each with 4-5 child pages.
All went fine until I got to adding the last batch of pages – the 6 x 4-5 set, when things started to go very slow indeed. Very slow, with Fatal timeout errors. I increased the ‘timout setting’ (sorry, I’m not a techie) from 60secs to 300secs, which solved the problem temporarily, in that it allowed more time for the server to do whatever it does and save the amended menu.
Now I’m discovering that even 5 minutes isn’t enough time . .

Help!

Looking at the HTML source code for the Menu page, I can see that each menu item comes with an enormously long ‘menu_item_description’ that seems to consist of the complete page text itself, which in many case runs to hundreds of words.
I suspect that this might be causing the problem . .
What do you think? Is there any way of deleting this unwanted and unused (in my case) bloat material? (Other than going into each menu item and deleting it) (which I’ve tried and which doesn’t seem to be working). Is this menu item description visible anywhere else, where I can scrub it away?

Any suggestions very gratefully received. I’m at wits end !!