I'm using plasma-workspace through an x2goclient (terminal server).
Plasma is after some weeks of mostly just sitting unused but the session being active using 1500 MB of RAM with 1200 MB being shared. I ksysguard I cannot find any other application that is sharing it as well.
I've saved a dump of "Full memory details" from ksysguard that I will attach.
Created attachment 81420 [details]
Plasma-desktop full memory details from ksysguard
This bug report was filed for KDE Plasma 4, which reached end-of-support status in August 2015. KDE Plasma 5's desktop shell has been almost completely rewritten for better performance and usability, so it is likely that this bug is already resolved in Plasma 5.
Accordingly, we hope you understand why we must close this bug report. If the issue described here is still present in KDE Plasma 5.12 or later, please feel free to open a new ticket in the "plasmashell" product after reading https://community.kde.org/Get_Involved/Bug_Reporting
If you would like to get involved in KDE's bug triaging effort so that future mass bug closes like this are less likely, please read https://community.kde.org/Get_Involved#Bug_Triaging
Thanks for your understanding!