Use either cache for large cross-site reports
If you report over a large number of site collections, it can take a while to process and render the data. If you switch on the Project Cache or Work Cache, you can improve response and rendering time in large reports.
Tip! To speed up rendering you can use either the views/CAML to reduce the number of items sent to the report.
Permissions should be managed in high level groups as much as possible, especially when it comes to updating either cache. Managing permissions in this way helps reduce the overhead on reading and writing data in either cache.
Gantt and Browser Performance
For display of medium to large Gantt charts, we recommend Google Chrome browser over both Microsoft Edge and Internet Explorer browsers for performance reasons.
Using Views/CAML filtering
Using Views/CAML filtering can give your reports a boost. Instead of filtering after rendering, as with reporter based filtering, use Views/CAML filters on the reports before they appear. If you start working with CAML, you can make some great speed increases.
Disable presence information in large lists
Presence is a SharePoint feature that pulls user information when hovering over their name in a list. This can be a handy feature, but can also be a burden when you have many users in a large list. You can disable presence on an individual web application to get a rendering increase. You can also disable presence on a per-column basis by editing a column and deselecting the Show Presence checkbox. You also have the option to disable presence in grouping.
Archive old sites
Older sites getting pulled in by large cross-site reports can impact performance. You can fix this by moving them into their own separate Project Area using the BrightWork Copy Site feature. You can also edit the project's BrightWork Settings and uncheck the Include Project Statement type lists in reports checkbox.
Slow report rendering has been helped with the introduction of the two caches. Another way to speed up reporting is by limiting the number of items displayed in a report. By reducing the number of items, performance will improve greatly.
Tip! Reducing the number of Groups in a report will also have a measurable impact when your report displays a lot of items. Having too many grouping levels may incur longer rendering times.