What is the saved file space needed for a typical Custom Recovery Image?

Reason I ask is my Lenovo laptop has a 15gb hidden partition... their famous one key reset, a magic reset button, that probably is broken now that I upgraded win7 to win8.
I'm thinking unhide the drive with PTedit and assign it a drive letter and wipe it clean first. If 15gb enough? too much ?

Hoping for some size idea before I waste time learning/experimenting.

Is the recimg program smart enough to not include full size paging file(16gb) and other non essential restores, hibernate(13gb) files.. which I have over 30gb sitting in those ?