Interesting that you keep saying you have this issue (previous one).
I still stand by the reply I gave to that one and I have to say that Krita made another nice step forward, in general but also in respect to responsiveness, with version 5 that was released in December.
GIMP still loads the initial project faster, but both handle about the same way when editing/composing. And that is using Krita’s non-destructive behaviour, which does come at a cost.