The age old question... to upgrade or not.  I have to say since SQL 2008R2 I lean to not.  2008R2 is very stable and I don't see any features for any newer version as a we can utilize that. Last fall my boss asked me for a list of which systems I would target to upgrade and the licensing costs.  It was very expensive to say the least.  We have a mixed bag here... many on 2008R2 up to 16.  It takes a LOT of man hours to upgrade a version with all of the testing that has to take place.  Not to mention almost everything we have are purchased apps so you then are tied to what the vendor supports, installing/upgrading the application and the testing that goes with that as well.  We have one system that we will be migrating from 2008R2 to 2016 by the end of the year.  The only reason is because that is what the vendor supports and to have full Microsoft support since 2008R2 will fall out of support next year.