I don't think we could really classify themes based on their system requirements. I'm not sure the average theme would differ too much from any other average theme. I have no idea what the requirements of my theme would be. I don't have the resources to test it on a variety of different spec machines and on a variety of windows flavours. And the modules I've used also don't make mention of requirements.

If you want a "low resource" theme then I would suggest creating your own. It's the only way to be sure. If performance it really a concern for you then I would recommend not using Litestep and using something like LiteShell instead. It's not configurable but it does everything you need and is about as small as a shell can be.