Bondware is still selling Poser 11, and is presumably still supporting it. It shouldn't be that much slower than Poser 2014. The system requirements are the same.

Superfly rendering is faster in Poser 12, but I haven't noticed anything else is. If he's having trouble with Poser 11 being slow, I don't think upgrading to Poser 12 would be any better. Something's wrong with his set up. Settings? Drivers? Something.