I have multiple GPUs and rendering a 1080p still image can easily take more than 15 minutes if we're dealing with multiple objects in the scene and possibly dark lighting (or multiple light sources) with reflective/refractive surfaces, etc. So, YMMV.
One thing ICSTOR typically does very well is that the animations show convincing, smooth motions for the bodies and they usually don't show major body overlaps or clothing/prop poke-throughs. I like MrDots' VN work but those defects happen in their products a lot, both for still images and animations.
Even if ICSTOR starts from canned motions, manual intervention is required to make them work tightly and without jittering between keyframes, especially when genital props are involved ... in my experience, that's really not easy with the tools available in Daz 3D, even if you purchased their AniMate, GrapMate and/or KeyMate add-ons.
Plus, all those custom scenes and the decisions+mechanics of getting poses right within them just adds up, to where the rendering part is probably not the lion's share of the time being taken. The better Devs are consistent in their quality for setup of every frame and that overall process just needs time. Some are obviously faster at it than others, though.