I am running VSCommunity 2015 in Win8.1 virtual machine installed inside a Parallels 11 virtual machine installed on my Mac OSX El Capitan. To my surprise and delight it installed and ran fine. I used it for 2 weeks without signing into my Microsoft account. I tried to login 6 weeks later and got the 30 day trial screen shown above.
However for me I was able to simply click on the link above shown as "Check for an updated license" and was prompted in to log in to my Microsoft account. I did so and it granted me a license successfully and was seamless. Now under License Status it displays as "This product is licensed to: ".
I guess I got lucky as I'm guessing this is how it is supposed to work.
[sidebar]:
Over the decades I've disliked most MS products but have been out of the VS IDE development tools game for awhile, and I have to say using VSComm15 has been flawless. Using it to learn C# and the IDE itself for a new contract job and it worked perfectly and has great features.