Hi,
It depends on how you use it.
First, as you said, there are 615,000 records. Do you need to show each detail in the report?Otherwise, you should aggregate, or better yet, use big data tools to do offline preprocessing, and the final report will show only aggregated data, which will be much smaller.
Second, because Knowage used anglajs for page rendering, you should reduce the number of widgets in a single document because the more widgets you have, the slower the page renders.In addition, you can use the BIRT engine for developing reports, probably faster than Cockpit.
I hope it helps.