Hallo2u
I installed a bunch of apps and still had room for more. If you're really so concerned about it then just head over to OpenEtna and get the stuff to upgrade to 2.2. You won't have the LG interface but, really, Froyo is better than LG's 1.5 anyways so it's win win.
Yes, you can go back to 1.5 if you need to.