Put a 3015LF in and use greenboy's passive sub crossover - available in the wiki.
It's not a big deal to have the 210 and 1x15 sharing frequency range IMHO, since the 3015LF will cover the majority of your range.
Another option would be to use Greenboy's crossover and add a midrange driver to the Peavey box, which it should have plenty of space for, or build a headcase, but the 2x10 should be fine.
in your second line are you saying that i may be able to run them together without the cross over or is this going to be required with the LF. i know i don't want to add a midrange, im, sure that would work well with the size of this cab and sound great but i'm trying to keep this simple. the 115 is never used on its own only with the 210. the 115 is only to add volume and beef up the bottom on bigger gigs.