Jira performance takes a fair amount of experience to nail down. If anyone needs help, that's what my companys (https://atlasauthority.com) core focus is. Spent 4 years at Atlassian in support, and now we work with a number of the largest deployments in the world to help make things fast(er). It won't ever get to the sub second standard we like to see from modern SaaS apps, but it also doesn't need to be 12s page load times like we often see in client environments.