Afaik, the only use of heal in ToEE is to stop someone from dying, an that's a flat DC15 according to the rules.
For curious minds here's the checks for various heals as per PnP, but as Ted stated the skill is merely a modified death save in TOEE. Task. Check First aid 15 Long-term care 15 Treat wound from caltrop, spike growth, or spike stones 15 Treat poison Poison’s save DC Treat disease Disease’s save DC Quicken recovery 50 Perfect recovery 100