For static scenes on a tripod, the usual choice is low ISO and a longer exposure. Lower ISO generally gives less visible noise, while raising ISO amplifies both the image signal and the sensor’s noise.

If you can safely lengthen the exposure or add more light, that usually improves image quality because you’re capturing more actual light rather than relying on ISO amplification. Since much of your frame is intentionally black, you can also let deep shadows fall to black and fine-tune black/shadow levels in post.

The main reasons to raise ISO are when you must shorten shutter speed to avoid motion blur, or when you can’t add more light. Many modern cameras are still quite usable at moderately high ISOs, but if noise is the priority, “spend ISO last.”

One caveat: extremely long exposures can eventually introduce their own issues, including extra shadow noise and heat-related sensor noise, so there is a point of diminishing returns.

In short: for your dark, mostly motionless scenes, start with the lowest practical ISO, use a tripod, add light if possible, and lengthen exposure before increasing ISO.