I haven't personally tried windows 10 operating system on 3 GB of ram since my computer has 8 GB of ram but I'm sure that Windows 10 will work on 3 GB of ram just fine since Windows 10 can technically work on 1 GB of ram although the computer will be slow.
I tried windows 10 on 1 GB of ram and it did install and I was able to use it but the memory usage was so high that the computer would start to slow down and it made things impossible to work with on the computer.
I decided to just upgrade to 8 GB of ram to be sure I would have enough ram for Video Editing and other tasks and Windows 10 runs really smooth with 8 GB of ram.
If you're upgrading Ram to 3 to 4 GB to run Windows 10 I would recommend just spending the extra money on 8 GB of ram because that way your computer will run smooth for a long time.
A slow computer is frustrating and can stress you out so get enough ram that you can to have a good computer user experience.