This article explains best practices for Power BI Jira Connector to avoid performance (loading time) issues.
Avoid any concurrent refreshes, i.e., Avoid refreshing two or more connectors simultaneously.
For refreshing the “History” fields, leverage the filter option to further filter history data.
If there is a lot of data, or if it takes a long time to refresh, you can split the refresh into multiple extracts based on the category or data.
Remove unused connector fields from the selection.
Limit to the minimal fieldset while choosing the performance-sensitive fields like “Sprint Metrics”, “Remote Links”, etc.
Limit to the minimal fieldset while choosing heavy data categories like “History”, “Work logs,” etc.
Microsoft suggests about smaller dataset refresh when the data model is bigger than 1 GB at https://community.fabric.microsoft.com/t5/Service/The-XML-for-Analysis-request-timed-out-before-it-was-completed/m-p/1964403#M133855