There are multiple causes that might contribute to the performance of Reporting:

• number of macros on the reporting page
• number of reports on the page
• number of pages being reported
• number of macros being reported
• complexity of the report

You'll need to consider how many pages do reports have to go through before generating each report. The performance issue can be vague certain times, as the performance of the server, memory allocated to Confluence, etc. will contribute to the performance of Reporting as well. As long the report is not taking a huge amount of time, or slowing down the performance of Confluence, it should be fine.

Another thing to consider is the usage of Content Reporter macro against Local reporter macro. The Content Reporter macro retrieves data from a large source, especially when @all is being used on the Space parameter, as Content Reporter will need to go through all Spaces before generating the report.