That encounter is a very tough fight. I will suggest you try adventuring somewhere else first and then come back when you are level 15. Have you been to Hiberheim yet? You can easily gain a few level if you clear that map and come back to do the immaculate test. I think most of the enemies in Hiberheim are around level 12 so it should work well.
I have absolutely no idea how you could reach level 13 without doing Hiberheim. I could try to kill the level 14 spiders in the area where I am permanently slowed down but that is equally not fun. Or maybe I should just look up how to enter the wizards house in Hunter's edge again but I definitely can not defeat the Rat King. He is level 16 I think.
There are several options for me but not one of them is fun. As far as I know there is NO area in the game where enemies have MY level. Wait, the goblins in front of the tenebrium mine are still alive.
