The Kubuntu team has just announced that the both the Plasma 5.5.3 desktop and KDE Frameworks 5.18.0 have been backported to Kubuntu 15.10.
One of the advantages of running Kubuntu is the fact that many of the new releases are backported to already launched distros. In this case it's Kubuntu 15.10, which only has a few months to live.
Kubuntu developers have been doing this for a long time, so people on this operating system are used with all of this backporting stuff. It keeps the distro fresh, and users get to experience the latest KDE packages.
Ubuntu and most of the Ubuntu flavors don't make big updates to the OS after the initial launch and only concentrate on package upgrades, but Kubuntu does things a little bit differently. It also means more work for developers, especially since the 15.10 branch only has nine months of support and it was released back in October 2015.
How to get the backported package to Kubuntu 15.10
As usual, this is done by adding a repository to the system. Of course, if you've done this before for previous Plasma backports, you won't have to do it all over again. Just open a terminal and enter the following commands:
sudo apt-get update
sudo apt-get dist-upgrade
The updating process shouldn't take too long, but make sure you reboot the system once the process has been completed. Enjoy!