Have you explored everywhere on sentinel island, and broken valley? I was almost level 16 at the end of Maxos temple, so you may have missed a few quests, or areas to loot.
Are you sure you checked all the traders (alchemist, black market dealer in the Black Boar inn, etc)?
You could head the fjords and hope for some random loot potions. There is one guy at the start that might have some potions, though you can not reach any merchants before getting the tower. Even if you don't get potions, you should be able to go up a few levels, which would reduce your need for potions (and IIRC the healing spell is available at level 17; level 1 is handy to have). I went from almost level 16 to level 18 in the fjords, and with the mindread in the first encounter on sentinel island, that brought me up to level 19.
In a pinch you could withdraw (in most situations, anyway) and just use food to speed up your healing. You should have 3 malachite gems by now; if you have found a high level healing aura formula (or an item with one you could un-enchant), adding that to several pieces of jewelry would help.
