Thank you for the hint. Adding additional repos usually results in a system that cannot be upgraded in straight forward manner to the next Leap release. Hence I rather avoid it. Upgrading to 15.6 did not work for that reason and I had to reinstall.
Another issue: Search in KDE‘s „Start Menu“ does not work satisfactorily. Incremental search stops after the first character entered, further typed characters do not appear as search is blocking it and stalls for at least 5 seconds before first search results are shown and characters entered are visible. Annoying.

I encountered a similar issue and resolved it by enabling the community Packman repository, installing OPI, and then installing the codecs from the Packman repo using the command "opi codecs." This fixed the problem for me. However, I agree that we shouldn't have encountered this issue in the first place.