If you're designing a trainer then why the laminar flow airfoil?

The whole point in building a turbine trainer IMHO is to build something that doesn't go that fast and allows you to learn the quirks of flying turbines. You want something that handles well at slow speeds and doesn't allow the speed to build up.

The NACA 65(2)215 airfoil seems unsuitable to me for a couple of reasons:
1) Sharp stall.
2) Good for higher speeds. Not so for lower speeds... At high AoA laminar airfoils really suck.
4) Low drag at high speeds. You don't have a prop slowing you down, you don't want it to get away from you.
3) Difficult to build. Hey, a trainer should b simple to build.

I would go with a simple semi-symmetrical/fully-symmetrical airfoil with a large LE radius. Something that is designed for slow speeds (Maybe S3016? S2027?)

15% thickness seems o.k. to me. You could go up to 18%. Just remember that slow for a turbine is still a 3 figure number in mph...