What's the fastest way to rebuild different sets that have been brought together
In order to gain value out of this, you're going to have to put some work in.

Start with the largest sized kit that you remember doing and assemble the parts (find the building instructions online).  Then move onto the next smallest, and so on.

Obviously, you're not going to remember the details of all the kits you had, but the largest ones should be more memorable (and usually they're worth more).