I saw the same complaints on another forum about a year ago.
It was a Pop Up Advert problem on the site, many adds & pop up banners slowing the page to load.
A couple of members on there said that everyone should install a free ad-blocker on their browser.
The one they suggested was
"Ad Block Plus"
You can get it free from this link...
https://adblockplus.org/
Very easy & quick to download & install, works fantastic, don't even notice it sitting on your browser
apart from the fact your pages are all much faster to load.
I have been using it ever since.
I just tried this forum with mine switched off & it was slow as, switched it back on & fast again.
I hope that helps.