Jira Cloud & Jira Server (on-premise) are two different beasts. I can speak for on-premise only. On my on-premise system which is located on the other coast of the country, a ticket loads in 1.5 ~ 2.5 seconds once your assets are cached at least once by your browser.

Things I've seen that can adversely affect your speed: installing random plugins that are poorly written, integrations, having too many admins over-complicating the Jira configuration.

Learn the keyboard shortcuts to speed up your basic operations.