I have this problem in Linux distros on my laptop HP Probook 450 G5. I'm using Firefox. Tried with Ubuntu, Ubuntu Deepin and KDE Neon - it takes between 10 and 20 seconds to load a website. Then I switched back to Windows 10 just to check and everything was fine. Now I'm on Ubuntu again.
Download speed is not affected.
The problem occurs with the initial loading of the site, then the other pages of the same website are loading faster.
My hardware spec
Bookmarks