I know i reached out to a kiltmaker here in canada and they won;t even make a lightweight kilt, and 13 oz is "if you want, but secretly we don't like it". Basically the 16 is the traditional material, the "proper" material if you're that traditional. It does hold the pleats better, which makes sense.

You just can't go wrong with a 16oz in principle. Other thing is that wool does breathe fairly well, as it has been documented elsewhere, the hose often have more to do with being hot than the kilt itself.