I'm seeing the same difference between Android and desktop Linux.
With my small collection of 30-ish notes across maybe five notebooks, the desktop client takes 3-5x as long to "synchronize" when there's no changed content (basically check the server for changes). Doing the same syncs after adding a new note in either client doesn't noticeably change the time it takes.
Edit: I should specify that the server is Nextcloud; not sure if this makes a difference.