|Hmmm. Maybe you should try to break down the problem into its pieces to determine where to make your improvement.
For example, determine how many miliseconds for each part of the process ...
1) read file
2) analyze data
3) draw graphs
4) present results to user
I'm not exactly sure how to capture each one of those statistics because I don't fully understand your application, but you get the idea. Determine which piece of the puzzle is taking the longest and then the folks here can offer you ideas on how to make it better.
Some other points of interest to post would be:
a) what version of IIS are you using
b) what browser is your client using
c) what kind of network connection is between your webserver and client (LAN/WAN), (10/100/1000) MB per second.
d) maybe a simple ping test from the client machine to the webserver could provide insight to a slow network
Good luck. Keep us posted of your progress and solution.