Sorry, I missed the fact that xenial is LTS, so it is still possible to upgrade some packages.
So putting my LyX developer hat on, I see three arguments for upgrading:
* LyX 2.1.5 fixes several crashes
* it is able to read files from LyX 2.2.x, as found in newer Ubuntu versions.
* we are very careful to avoid introducing new bugs in our stable series
Sorry, I missed the fact that xenial is LTS, so it is still possible to upgrade some packages.
So putting my LyX developer hat on, I see three arguments for upgrading:
* LyX 2.1.5 fixes several crashes
* it is able to read files from LyX 2.2.x, as found in newer Ubuntu versions.
* we are very careful to avoid introducing new bugs in our stable series
What has to be done for that to happen?