Hi Deepak

If you want to share your code, you can do it via a free file delivery service. Google for the expression "upload your files" to find some such.
If I were you, I would compress your file into a password protected zip, upload somewhere, and post the download link here, along with the password.

Although, the "15000+ lines" is somewhat scary, someone might be willing and able to help.

Other than that, here's a layman's advice.

Scatter around some code-suspending messageboxes in your code, preferably into key positions, like before and after calling a large subroutine, or after every 1000 turns in a long running loop, etc.
Then open task manager, switch to process list, highlight Excel, and start your macro. Watch how Excel's memory consumption changes. Maybe this way you can delimit the problematic part of code.

Jimmy