I think it advises you be 15-20 or so, but that might be a bit low, really.
If they didn't steal all your gear at the very start of the campaign, with no way to get back to the Mojave until it's over. In DM, the Ghost People, traps, fucking sensor things, (some of which can't be destroyed and pretty much require you to noodle out their locations through trail and error) some more traps, and death clouds might all be manageable. Click to expand.This is pretty much the order of ascending difficulty, too, Dead Money and Old World Blues being sortof interchangeable.