I am a KDE Plasma Lover and I consider it to be the best DE available . But all KDE apps seem slower to me . Even starting the apps takes longer . i.e. It takes longer to open Dolphin than Thunar , Spectacle takes a little while before taking a screenshot than gnome-screenshot . Even the Settings Manager( systemsettings5 ) takes some time to open .
So my question is
Why is KDE Apps slower than others ?
I just need to know if it’s only my problem . For example thumbnail generation takes longer in Dolphin than in Thunar , others have also experienced this . Hopefully an upcoming update will solve this . But opening Dolphin takes almost twice the time to open Thunar . So I compared other KDE apps with other DE’s preferred applications and found out spectacle takes more time ( almost a second ) to take a screenshot when it’s set to take the screenshot instantly . While gnome-screenshot takes much less ( maybe 300-500 milliseconds ) . konsole vs xfce4-terminal gave the same result . xfce4-terminal opens almost instantly .
One can say booting into Plasma Desktop takes longer because Plasma brings more dependencies with it . But what about taking a screenshot . This slow behavior is the only reason why I had to go back to XFCE before .
My friend also had this experience . And of course it annoys me a lot . I just love Plasma so much to see it lagging 
Edit : It slows down randomly i.e. sometimes slow , sometimes not