Alright.
I made some further tests. Same exact scene on 27.17 and 28.6
I took some time to adjust all the shaders to 27.17 then saved it and opened it back up in 28.6 to do the test there.
Scene in 27.17 send to render. Time in between frames, still a rather long 60 seconds.
Though massively faster then on 28.6 where i clocked it pretty exactly to 120 seconds.
Also It takes less ram to prepare the frame on 27.17 (not Vram, system RAM)
Hopefully it´s not annoying me comparing it with my C4D experience all the time. I have the feeling that in C4D, like in Blenders "Viewport Shading" / Live rendering the delta is streamed to the engine every frame. But with blender there is something more going on. It needs to update instead carrying on rendering.
Also I tried making a viewport rendering because that would mean fast rendered previews. Unfortunately this did not work and the preview was all dark gray (I guess the viewport background color)
Cheers and thanks again for reading about me rambling on!
Raphael