Windows 10 will run on a vanishingly small amount of system RAM, if you engage in some trickery, and don’t mind that the operating system isn’t actually usable running in this state.
http://www.techradar.com/news/windows-10-can-actually-run-on-a-tiny-amount-of-ram-just-192mb
http://www.techradar.com/news/windows-10-can-actually-run-on-a-tiny-amount-of-ram-just-192mb