First of all, from my personal experiences, hair props/characters may explode the render time.
Here is a portrait, created at the same dimensions as your picture, using Poser's default "Ultra non-branched (GPU)"

The hair is Aeon-Soul's Desir hair, which is time-consuming during the computations.
My GPU is an old RTX-2080Ti and it took 13 minutes using the Optix mode, probably near twice longer using the default mode.

No lights involved: only an HDRi on the background node.

From what I've read online, your 3090 should be at least twice as fast. Even though you have a pretty fast CPU, your video card should kind of shrink the render time down to a microscopic level compared to the CPU. I mean: the first time Poser12 supported the 3090, the crew did a test with a scene, it was something like 5 to 6 minutes for the CPU down to 10 seconds with the 3090... (these aren't the right values but that gives ou an idea)

That's why I'd like to say: check the following points.

First, check the video card's drivers. I never used NVidia's default driver, only the Studio version. The standard version is often a nightmare in terms of stability...

Then, something else I've remarked: if Photoshop is loaded, with a scene and not minimized and "empty", as it can use the GPU as well, I can see a real difference during the computations: consider this as well depending on the other programs you are using in your process.

Last but not least: I suppose that you're on Windows. Don't forget once you know that you'll made a series of computations to restart your Windows station. Don't turn it off/on: reboot, it will refresh its resources.
Example: for my job, I'm using PyCharm, which is a real resource-hungry program. After a few days of using up to 3 instances of PYcharm, 1'234'567 tabs/windows of different browsers etc..., rebooting my PC makes a really noticeable difference depending on what I've been doing during work hours (I'm working at home on a browser-based python-written framework)

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