ORIGINAL: vertical grimmace
An NACA0013 would be a great airfoil on that little Ultimate. I guess the key aspect of a good design with a fully symmetrical airfoil is wing loading. It is imperative to keep them light and then they really come alive. The main bonus of the Ace wing though is how easy they are to build. They would certainly do a little better if they had a spar installed as well. they are just not stiff enough to be precise.
It's easy to route in a spar, even on a table saw if nothing else. I've also capped mine with 1/4" strips of unidirectional .003" CF in a sanded slot, and they pretty much don't flex under reasonable loads. I imagine one could cap or spar the wing, then cut out some material from the outboard "rib bays" to save some weight.
But yeah, they are not the lightest option by any means, only convenient. But they work for knock-about sport models. Nor is the 2415 maybe the best airfoil for small models either, too thick IMHO.
Vertical Bearded Grin - here's an overlay of the 2415 and 1415 for giggles. Not much saddle filler needed to adapt.
MJD