SQL 2012 is out of support and has been for over a year. 2014 will be out of support next year. Upgrading to either of them at this point in time is a bad idea, and there are many compelling features in 2016/2016 (Query Store!)
I recommend that you speak to those vendors about getting their apps certified on 2017 (or see if they're happy with them running on 2017 in an older compat level), and upgrade to 2017.
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)SQL In The Wild
: Discussions on DB performance with occasional diversions into recoverability
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We stand on the bridge and no one may pass