I know what you mean, my pc struggles a bit, I've got a titan rtx card but everything else about my pc is just average so it takes a while to load and save some scenes, my rendering times aren't too bad though, usually takes around 90 minutes for each image
I want to share my workflow for some bigger scenes with you. Please ignore if you have known already.
1) I use
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to lower the resolutions of textures visible in the scene. Usually, my maximum sizes are 2048 and the minimum ones are 1024 or 512 ( if that is the original resolution of that texture). There is no rule but the goal is to keep the scene loads not more than your GPU's Memory. Mine is 1660 super 6GB, so I try to keep my scene lower than 6GB. By doing that your computer will never ask CPU for a fallback. As a good consequence, you are 100% okay to turn Denoiser on. Otherwise, if your computer asks for CPU for help while rendering, there will be no Denoiser punching in even though we turned it on. I know using denoiser is hurtful but denoising later in photoshop is more hurtful.
2) In render>Progressive Rendering, Rendering Quality Enable must be turned on, if you want to use denoiser.
3) Putting Instancing Optimization from memory or auto to Speed is optional. But every little help.
4) Finally, set Noise Degrain Filtering to 1 to avoid white grains.
Below are 100% must
Point Denoiser Available = On
Post-Denoiser Enable = On
Post Denoiser Start Iteration = 8 ( This is the best one, I can tell you from some experiments I have done in past)
Post Denoiser Denoise Alpha = On (this is optional)
With Post Denoiser Start Iteration = 8, you can see the result at the very earlier stage and can decide when to stop/cancel you render. Otherwise, for example, if you set it to 500, then you will have to wait till 500 to see how it will look like with denoiser turned on. With lower number like 8, the result can be seen quite well starting from like 50 for most cases.
One last thing to do before rendering is:
5) Disable Allow CPU fall back and uncheck CPU under Rendering/Advance tab.
This will make sure to let you know that your PC will only be rendering with GPU which is a lot faster than CPU does. And Denoiser will surely be turned on if you lowered texture maps to suitable sizes according to your GPU's Memory Usage.
Hopefully, most smaller scenes are usually done rendering within 1-2 minutes for me. The bigger scene takes 20 minutes at most for me.
If possible adjusting exposure under tone mapping (don't take it wrong they are also necessary for pre-processing work to look better than natural) to brighten the scene will not speed up your rendering, it just removes the grains like ISO work on a real-life camera. If your scene is dark, the first thing to do both in DAZ studio and in real-life is to add lightings. Try adding emissive lights, surfaces (sometimes called ghost lightings) if you don't want to end up spending your GPU usage with point/spotlights. But from the POV of photography using a wider diameter lighting source (Both on Spotlight and Emissive Surface) or filtering the light with soft white/yellow plane surfaces will make your scene look like Hollywood standard in my knowledge. Softer shadow edges mean a great work of Gaffers in the shooting. But I am sure it will be optional for scary/creepy scenes.
I hope it helps. Thank you for reading.