Matt,
RCCA has three classes that use .15 singles: Open A, Scale 2105, and SSC. The max weight for Open A is 2.5 lbs and the folks who fly it claim to build to about 2 lbs or slightly less. I've not seen a 2105 plane so somewhere will have to step in and answer that. The SSC planes with 60-70" wings have a minimum weight of 2.5lbs and are up to 3 lbs 3 ounces. The SSC planes although heavier generally have lesser wing loading.