Query strings definitely won’t cause that kind of load time.
I also highly doubt it’s GP, as it would be happening to a lot of sites, including this one.
I actually just wrote a post on optimization, you can find it here: https://generatepress.com/fastest-wordpress-theme/
There might be some tips in there that help you.
However, if I had to guess, I would say one of two things are doing this to your site.
a) Some rogue plugin you have installed. Try installing a plugin called “Query Monitor”, it will spit out any errors which might be causing the issue.
b) Your server – load time is highly dependent on your server/hosting. Shared hosting can be brutal, as it could be another site on your server (someone else’s site) hogging up all of the resources, slowing your site down.
You can contact your hosting to see if they can see the issue, and if not, you can request that they move your site to a different server.
Hopefully this helps – slow websites are frustrating.