Seems Lightroom is taking time to generate previews.
Go to Lightroom Preferences > File handling > increase the camera raw cache size to 70-80GB > quit and relaunch Lightroom and then, check.
I can't view your video. I get the message "Whoops! There was a problem playing this video"
I'm new to Lightroom, but this software is either bloated or stupid.
There are plenty of other possibilities, including conflict with your operating system (which are usually easy to fix), conflict with your hardware, and user error.
Thank you Chetna. Performance is slightly improved since expanding the software's cache size.
Still some things are slow, but the folder-loading video I shot seems less frequent since enacting the cache increase.