1. USE your own choice of DNS. Many ISP DNS's log where you go and are just slow.
I use 126.96.36.199 and 188.8.131.52 Google "How to use your own DNS" if you need more about this.
2. I take it you don't have a big security package or suite. Some navel gaze and degrade the response time.
Try a clean browser. That is, one that you have completed step 1 and for step 2, reset that browser.
I have a little bit older computer (8.1) with plenty of memory. I leave too many windows and programs open at a time, but I always have. My computer crashed recently and had to be re-done completely. So, everything should be pretty clean. Also on this WiFi is another computer and a laptop. We do no gaming and the only streaming we do is youtube.
This computer is slower than molasses in the winter time. According to speed tests (I've tried several) I'm getting 220 to 290 mbps depending on when I run the test. It makes no difference whether I use WiFi or ethernet, it's still slow. I can inquire of Mr. Google, and it can take a full 5 seconds to get a response. Same with checking my Yahoo mail.
Are the tests correct? If so, why does it take so long to get a response?