Hi,
I wish you had tried the demo in such cases, as its aim is to determine performance impact on one's system. There are several community presets for better performance, which you can find in the Discord server. If Discord isn't your thing, you can look at the documentation which explains performance-critical parameters in the settings.txt (skip_fragments, maximum_drawing_distance and resolution_ratio) and modify them for your liking.
Performance impact inside cloud layers and / or multiple layers are expected as this is the time where virtual rays has to traverse the longest distance, hence increasing the performance impact.