[frankywoter]

I used Kodi 14 on Ubuntu 14.10 without any issue. I upgrade (just update without installing any additional plugins or skins) recently to:
Kodi version: 15.0 and now 15.1 Git:d496682
Ubuntu 15.04 kernel 3.19.0-26

Kodi 15 user interface keep freezing for milliseconds (but noticeably) when I move around menus. This occurs for every two or three keypress. It's very annoying. For example I select position in any list (you know, background and text are both highlighted) and press up/down arrow key. First moves the background highlight (meanwhile GUI freeze for a moment) and after that second moves the text highlight.
Another but I think related issue. In details window when text is longer than window normally text smoothly moves up. In my case text move two lines up and stops for a while, moves up and stops, and so on.
Playback is always smooth. CPU and Memory usage is not a problem.

[frankywoter]

After update Kodi to 15.2 RC1 problem still occurs.

But I noticed this behavior gone when switching Kodi from Fullscreen mode to Windowed. If switched back to full screen GUI once again become occasionally unresponsive in the manner described in previous post.

[un1versal]

Debug Log

[frankywoter]

Problem solved. Of course, driver issue.

I needed to purge (not only remove) fglrx driver. Now the opensourced radeon works flawless. My bad, I should read manuals more precise about fully wipe out fglrx before try another.

I installed fglrx before because radeon made Ubuntu 14.10 very unstable.

[un1versal]

fglrx is unsupported in any case.