As removal of independent wallpapers for each Virtual Desktop is quite heated topic and KDE5 tells me that no, I won't have it and I need to use Activities (viewtopic.php?f=67&t=141878) I decided to give it a try as using KDE4 on modern distros is more and more difficult due to EOL state.

So I created Activities instead of Virtual Desktops and now I have different question and different problem - how do I change animation speed of Activity slide? Because default animation is so extremely quick that my GPU stutters too much and I don't really have any particularly spectacular animation, just 2 random frames.

This animation is terrible in general to be honest and it only works for plasma because windows just disappear in 1 frame but I hope longer duration would help a bit at least...

Maybe try the settings in:

System Settings>Hardware>Display and Monitor>Compositor