you want to test using --vfs-cache-mode-full, that way rclone will only download the chucks requested instead of the whole file.
as for the click right mouse click, you can figure out which menu entry is the problem.
using one of best set of windows utilities - nirsoft
https://www.howtogeek.com/684164/how-to-fix-a-slow-context-menu-in-windows-10s-file-explorer/