You shouldn't have any issues introducing a Server 2016 into a Windows Server 2012R2 domain. This is a totally regular operation.
First of all, I would recommend to run a DCDIAG command to check the health of your current DC before promoting, after that just follow the usual promotion proces. I would also recommend to add the DNS role into the new server and make it Global Catalog, for redundancy.
You can find some guidelines and screenshots of the promotion process here: https://learn.microsoft.com/en-us/windows-server/identity/ad-ds/deploy/upgrade-domain-controllers .This may also help you in case you wat to rise the Functional Level of your domain to 2016, keeping the 2012R2 as secondary and 2016 as primary.
Hope this helps in your case,