Whew. At 8 seconds I'd probably call for the tool to be removed. I had a similar experience while at Atlassian at one point and then we found a way to speed up the (Jira Core) boards by ~5 seconds after changing some JQL for the board logic. That change should be in effect for your org but you'd need to use Classic Business projects.

Fun fact, next-gen might actually be a reason why your instance is running slower. A side-effect of NG can be the slowdown from each project with its own custom fields and that effect multiplied hundreds of NG projects across an organization. Then (I think), when loading your project it calls all the fields to see which fields it should show. Not an ideal rec, but I'd check out Classic projects and see if that speeds things up for you and your org.

Speeding up Jira Cloud is a top priority for Atlassian this year so you should see some improvements coming. I'm working on a new view right now in Jira and we've been able to load about 100 issues in ~1-2 seconds. It lazy loads, but we can flip through 500 easily once you've scrolled to the bottom. Should be able to get that in your hands this coming year.