For the third time my KDE Plasma Workspace has failed during the post-installation software update. On the third occasion (but not the other 2) it managed to display an error dialogue box, though I could not send a bug report directly since the system hang had disabled the mouse and keyboard. However, the dialogue box contained some information which may be of use to you:
"Plasma closed Unexpectedly"
"Executable: plasmashell (deleted) PID: 2204 Signal: Segmentation fault (11)" [followed by the date and time]
[The software update (comprising 696 items) was about 75% complete according to the progress bar, and was well into the installation phase. My system is based on an Intel Core I7-3770K CPU and a UEFI 'BIOS', running the 64-bit version of F22. It is not dual-booted (I run Windows most of the time - such as now - but had hoped to run LINUX on separate disks).]
I would be delighted to run KDE Plasma Workspace, but I can't afford to waste any more time repeatedly installing it: if you can't produce software stable enough actually to install successfully, I'm surprised anyone is able to use it.