We do rebuild the whole archive [1] before release so updating while updating glibmm now would not cause anything to break due to ABI all the packages that build against it and don't use C++11 would be marked FTBFS (fails to build from source).
Note that only glibmm could be updated since we have the latest glib. The rest of the mm stack would have to be running the pre-C++11 versions. It will probably be easier to update everything in 16.04.
We do rebuild the whole archive [1] before release so updating while updating glibmm now would not cause anything to break due to ABI all the packages that build against it and don't use C++11 would be marked FTBFS (fails to build from source).
Note that only glibmm could be updated since we have the latest glib. The rest of the mm stack would have to be running the pre-C++11 versions. It will probably be easier to update everything in 16.04.
[1] http:// people. ubuntuwire. org/~wgrant/ rebuild- ftbfs-test/ test-rebuild- 20150202- vivid.html