I now know from first-hand experience how well Windows 10 runs with only 2.6 GB usable RAM.
Answer: Not well enough to remove the preinstalled McAfee trialware, and just barely well enough to remove it with the McAfee removal tool inside two hours.
Everything else is an equal test of absurdly extreme patience. More frustratingly, it struggles so much to recognize mouse clicks that the only way to tell a click was acknowledged is the window suddenly freezing for many seconds.
That budget Win7 PC is so budget that it has a single Allen socket cap screw (CR-V 2.5) holding on the side panel, a 2GB RAM stick, and a 1GB RAM stick.
As you could imagine, Win10 performed well enough to actually install updates when the super-cheap 3GB RAM was replaced with very affordable 8GB RAM.