It should not be because of a RAM difference between the machines. If anything, you may be maxing out the 16 GB machine. I've been using my small farm and Team Render with Macs and PCs, 32 GB, 72 GB and 128 GB RAM, plus all different CPUs and I still get great results. Now I understand some of my machines are stacked with RAM, but if a client runs out of RAM, it should try and swap to virtual RAM and use the hard drive, which is of course, much slower. If you then run out of HD space, that's another issue.