Hey thanks a lot for your advice !
i've switched to EEVEE and it's a lot better, plus everything was running on my CPU so ofci t was horrible...
I think I'll soon update my whole HW, maybe like end of August, try all the new shiny things that will help me. I have like 32 Gb of RAM but I'm afraid my GPU is the limiting factor for everything...
Thanks again for you help ! Even if not perfect, things run a bit more smoothly now !