Website Data Loads Slowly

You can make "Loading website data" faster if you empty caches first.

Safari > Preference > Advanced

Checkmark the box beside "Show Develop menu in menu bar".

Develop menu will appear in the Safari menu bar.

Click “Develop” to show the dropdown.

Click "Empty Caches" in the dropdown, give it a minute or more.

Click the button twice. Test.

if you want to keep cookies of particular website you have to search in safari > preferences > manage website data select and don't remove it .

As you already said it took hour's to clear cookies as there may be many cookies saved from months .

Also , you said you don't want to delete cookies for particular website , it is very tedious job to search cookies for particular website .

So , to clear it immediately and speed up the process of cleaning cookies is take cursor on top menu bar click on history > clear all history & website data .

This will remove your browsing history & cookies saved for the all websites that had been saved in your browser .

Note : it is recommended to clear history & website at the end of the day .

I see the same thing and no one has posted a workaround to speed things up.

Send Apple feedback. They won't answer, but at least will know there is a problem or a suggestion for change. If enough people send feedback, it may get the problem/suggested change solved sooner.

Feedback

This works!!