Just viewing images in detail view Lightroom is using 9Gb or so with 9gb swap used. Doing any editing LR is using 11-14gb and swap goes up a little to 10gb or so used. Physical memory used stays around 7gb. Is that heavy swap usage?
That's with only Safari, LR and activity monitor open.
I would say that is heavy swap usage, yes. (Although to understand you actually need to look not at the
amount of swap being used but how actively swapping is in and out)
I don't have an M1 yet but have been following what other users are saying about usage on Lightroom. Short form, it does not seem to be optimized for M1 yet, possibly because Adobe is using some bespoke graphics/memory handling approach (i.e. it's not just a recompile issue) that doesn't play well with M1.
Strong suggestion: go into the preferences/performance tab and try different settings for the use of the graphics acceleration (including custom, turning some of the settings off and on). It seems that the accelerated graphics is in some cases duplicating memory usage and presumably bandwidth (without getting any benefit from that with M1 memory/graphics approach); and that the native Apple/MacOS frameworks don't run into this issue.
Frankly it's disappointing Lightroom hasn't been updated for this yet (assuming you're using the most current).
But still: Lightroom is always going to be memory heavy and likely to benefit from the 16gb. Even browsing thumbnails uses a lot of memory.