There is a way to improve the quality of pre-visualization? in the preview I have this very low quality black pixels, in the example It's much better. There is a way to seepd up the pre-visualitaztion. I have 32 GB of RAM and a i7 9 generation intel...
Here mine:

Here the example:
To get rid of the noise in the viewport, you can increase the Viewport Samples, and/or turn on Viewport Denoising (denoising will provide comparable quality, while allowing you to get away with using fewer samples):