Yep using G8, however have now removed everything that isn't in the line of sight and reduced / removed some of the textures. With these adjustments the memory now being used is just below the capacity of the graphics card and successive frames are rendering at the same speed. Despite having increased the iterations to 50 per frame it has completed 15 frames in the last 47 mins, so I think it is sweet now.4.8 gb vram for this simple scene is a lot! Not to say way to much. Let me guess, you use g8?
If you have other assets in the background, remove them completely. The wall in the background is far enough away to remove all, but the base color maps, if there are any. The ground looks like it could be compressed further without loosing too much quality.
G8 has a lot of unnecessary textures you only really notice in closeups:
If there's a map in any of the "Glossy" channels, remove it, same for "Top Coat" and "Metalic Flakes".
The clothes can be compressed further, you won't see many details after denoize anyway.
You could try the camera mentioned in this thread. I've used something similar a few times. It obviously changes the light a little bit in some scenes because it uses iray section planes, but it's not really noticable and worth it most of the time.
If this still isn't enough, you could try the batch render that was mentioned here several times (the one that restarts Daz).
aaand if nothing helps, render the background without the girls one time and then the animation with the girls with only the blue.... thing on the ground (I don't know how it's called in english^^).
What I would note is that when going from frame to frame it seems to be reloading textures, however memory usage changes from 4.6GB to 3.0GB and then back to 4.6GB. I'm guessing is that only a portion of the textures are being reloaded, however it may also be the source of the issue.