You seem to have a very powerfull Tableau Server.
It seems to me that you database is slowing everything down. Have you tried working with extracts instead of a live connection?
You can also always check this:
i've tried to create extract but it takes too long.
Maybe it's time to upgrade the database
Thanks for the reply btw
Have you tried creating an extract with the option "Hide unused fields"?
This already makes it way faster!