I duplicated this vault (741MB) into my Downloads folder (local to the laptop) and I am unable reproduce the delay.
Hopefully this is a temporary side effect of the MacOS15 beta build profiling. I will file a bug with Apple against this new “Keep Downloaded” feature.
The use case is important as “Optimized Mac Storage” is necessary due to space constraints but obviously some data needs to be kept consistent locally. Thanks for looking at this and the duplicate suggestion.