after effects preview freezes

A two hours long comp? seriously? AE is not an editing sweet and meant for short clips/ shots. Of course you will eventually run out of resources and AE just lock up, be that glitches in decoding the files, running out of RAM or the cache filling up. I feel there's really no point to further discuss this. At the very least split up your comp in shorter segments that you relatively low end computer can handle separately, but even then you'll likely have to make it a habit to regularly flush out the caches.

Mylenium

Without any exact system info, details about your footage, comp settings, preview settings, cache settings and so on none of that means anything. You need to be much more specific.

Mylenium