Other PRD clients generate slower reports compared to main

Good day experts,

I have PRD clients A(main) and B(test) on a server. Client B has lesser data than client A, but client B generates report slower than client A on some reports. I have observed that on tcode F-03, it stays on table RFBLG for more than 500 secs then dumps the report on client B. Another observation is that, on custom reports, upon getting data from database, client B is faster, but when it comes to processing the data before output, there is when client B stays for quite a long time.

Any inputs on this?

Thank you in advance!