I was almost level 16 at the end of Maxos temple. Before the temple I was level 14 outside, but entering completed the Paper Trail quest, which brought me up to 15.
The majority of opponents in Maxos temple are about level 12. It isn't so much the level that matters (though the final fight in the temple can be tough if you are too low), just that at some point you will not be able to complete any quests in Broken Valley (you can return to the quarry, but most other locations and NPCs will not be available). It would be better to finish everything off before moving on to the next area.
You can go to the bandit camp and take part in the raid (for some experience and loot), but you will not be able to do the couple quests there. I think you can still enter the temple, though (not sure).
