Jaya, Reading all responses from fellow friends, makes sense that nothing makes sense. It does make sense? Perhaps not, please, let ma ask you more questions:
If nothing (network, DB) is different between the two environments but SAP version, I would troubleshoot with the following list:
Do the reports have prompts? Sometimes default setting in new installation force to refresh the LOV (List of value) each time reports run with a prompt and the delay occurs before the windows asking to asnwer the prompts appears.
In the original environment, the PRM fles were modified: New install cause to install default PRM files that governs the way the SQL is generated. Please check the SQL statement in both environment is the same.
As third option, I would try to run the report(s) in Webi Rich client (Two tierds mode) from the server and see if the execution last as long as when executed thru the web. If the execution in 2-tier moe is the same in both environments then I would double check web server version (and If tomcat) Java versions.
Nothing else comes out of my mind at his moment. I hope those little drops can help your cause.
Good Luck!