I would like to ask whether a request object with so much data and getting that data from request object in JSP is a heavy process? If yes then which one will take less time. Using request object or using scriplets and call java methods from JSP? I know writing java stuff in JSP is not a good design but this application is quite old and we are not allowed to change anything . We are trying to make Minor changes to improve the performance.
Guessing won't do anyone any good. Get a profiling tool (no, I don't have a recommendation -- do some searching) and find out where the problems really are. Doing things like "maybe it'll be better if I use scriptlets" will not get you anywhere. Find out where the real problems are and then fix them.
P.S. 9 times out of 10, the database and queries run against it are the biggest performance hog in a web app.