Except under extraordinary circumstances, bug fixes go into the current or future release streams only. We will accept support inquiries about the previous two versions, but bug fixes almost never are put back in older versions. (The exceptions are typically for large ISVs which have a contract with us for extended support.) Often, shortly after a new release comes out (such as 16.0), there is one last update to the previous release (as is the case here - there will be an Update 6 to the 2015 product, maybe not on all platforms), but the set of fixes that go into these is extremely limited.
