is it true that such scenes are difficult to render?
It depends on the lighting, and how many characters you have in a scene. If you dial everything up and put a big ass light in front of them it will render faster but it will look like shit, so I like to use different a darker more naturally lit environment so it looks better but takes longer to render. And it's not that long of a render for 1 frame (1 image) but for the whole animation mine for example the fucking animations have 90 frames (images in them) It's still a loop but in order to make them look more alive many details are in it arms legs moving etc and it can't be done properly with less frames. It takes me 10-12 hours to create 4 animations, but takes a lot more to render them. However blowjobs, boobjobs, footjobs, handjobs those are much simpler and those are done really fast.