After upgrading to Kubuntu 15.10 from 14.04, I've found that some programs get much slower or completely hang over the course of a few hours of use. (Even though I have 32 GB RAM, an SSD, and a fast 12-core CPU.) Examples:
Imagemagick operations, like "convert -resize '35%' largefile.jpg smallfile.jpg", simply hang. Likewise for "display largefile.jpg".
I run "geeqie" to view a directory full of photos. I press the down arrow key to move to the next photo. Nothing happens and geeqie is frozen for about 20 seconds, then it unfreezes.
Google Chrome slows down considerably and freezes frequently, then unfreezes. I visit a familiar web page and the scrollbar doesn't function for the first 10 seconds.
I run Terminal by pressing a hotkey I defined (alt-ctrl-T), and the window appears 15 seconds later, or not at all.
"top" says that nothing is hogging the CPU. "free" says I have 28 GB of free memory. My instinct says "blame Plasma or sddm."
The problems are intermittent. But when I log out of Plasma and log back in, and everything's fast again. For a while.
14.04 worked like a charm. Very frustrating!
Any tips appreciated!