Yes.Can the 10.2 Preview be installed with a 10.x License Key?
Yes, it's the same branchAnd is it able to be upgraded to the full 10.2 Version, when released?
Upgrade from this preview version will not be supported by further versions.
Because when you install a new server, it's strongly recommended to use the stable version of an OS.Sorry, but I do not understood why supported OS is so important? There are other supported OSes...