Enough talking of the lackluster release. To upgrade from my 15.04, just type this command. Depending on the existing installed packages and your network speed, it took me around 3 hours to download all the required packages.
$ sudo do-release-upgrade -d
Once all the packages have been downloaded, answered a few questions, and wait for an hour to upgrade all the packages. Restarted my laptop once done. The upgrade was painless without any hiccup compare to past experiences. Is it because I'm using GNOME instead of Unity desktop? Doubt so, but based on my painful experience of getting both GNOME and Unity to work side by side, is best not to venture into that.
$ lsb_release -a No LSB modules are available. Distributor ID: Ubuntu Description: Ubuntu 15.10 Release: 15.10 Codename: wily
However, the annoying Internal System Error popup still persisting, which is due to gsj-console. I'm not sure the root cause of it but decided to disable it permanently.
$ sudo sed -i 's/enabled=1/enabled=0/' /etc/default/apport $ sudo systemctl stop apport