I would suggest for you, to install Calibre directly from the official Website, if you want the latest improvements.
(The latest release of Calibre is 3.19.0.)
On Ubuntu (another Linux distribution which I use since around 7 years now) the packet-release is around version number 2.5, too. And it bothered me. xD
Problem: You have to update manually every new Version.
Plus: Latest improvements (for example the Split-Screen).
Sorry for the bad English grammar and the off topic.