Dno, I started temple at lvl 12,
there s lvl 13 mobs spawning,
but you can always leave, once you are through the first room there will be a waypoint shrine. There will be another one deeper, right before Amdusias. Also gates always open again after finish business. Just save often enough and you will be fine. It's quite obvious Maxos temple is something "big", should ring a bell to save game before entering smile.

What I did in short:
I for one was lvl 13 when I could encounter Amdusias, but it was too difficult, always one-shot me with his magic.

So I decided to finish some side quest n kill some things I didn't kill yet in Broken Valley.
Got me to lvl 15 as I was hoping for. Got me the very powerful boost on magic blast (lvl4), got me hide in shadows and fire wall lvl 1.

Killed Amdusias without getting hit :o, magic blast (stuns him a bit), jump backward(so I'm out of "sight") n wait a bit, hide, run forward next to him, wait a bit(cooldown magic blast leftovers), firewall and magic blast, that did it ^^.