I’m guessing this is being done with something other than our Community Events plugin?
If so it’s hard to suggest really concrete measures as I don’t how your solution works – but would encouraging the user to search for pre-existing venues in the first instance (or only exposing pre-existing venues) be an option?
Perhaps you could create events and venues separately, but use post meta data to establish a bond between them such than on approval or publication of the venue it is instantly linked to the relevant event?