IR/LC very noisy when downsizing render resolution?

[fraggle]

Hello, I precalculate LC/IR for a 6000x6000 pixel image.
I would like to make sure the Renderfarm will work as expected before submitting the 6000x6000 by first lauching a 600x600 pixel render.

I test it on my workstation first, but the result is 10 time more noisy than on the 6000x6000 pixel.
Is it normal to get a noisier result on smaller render size image when the LC and IR map have been calculate for a bigger size?

Thanks

[fraggle]

Here is the same scene render at 6000x6000. Still noisy but the noise is smaller.
The noise is coming from the HDRI dome. I hope the denoiser will work fine on it without destroying the details.