Thank you pjz99, that is certainly a very good point. I am using purchased skin textures and they are all very high resolution. Two of the characters also have strand hair applied. As it happens I got this particular scene rendered after numerous attempts. Perhaps I should make medium and low resolution versions of the skin textures for scenes where the figures are not viewed in close-up.

I considered using face room textures, but getting the face and body colour to match is something I just can't get right.

Perhaps the answer is to resample the textures. I am going to try that.

Poser 11 Pro, Windows 10

Auxiliary Apps: Blender 2.79, Vue Complete 2016, Genetica 4 Pro, Gliftex 11 Pro, CorelDraw Suite X6, Comic Life 2, Project Dogwaffle Howler 8, Stitch Witch