Did you look at the log? Anything strange there.....?
Also, is anything else slow?
Can you create a NEW OGM ( not a copy) and check to see if that is also behaving slowly?
Any other OGMs slow to respond as well.
You mentioned that there is nothing else running on the server....try having the task manager up when you are inputting the numbers, and check to see if there's any unusual spike of memory or cpu usage at that precise time.
If all else fails, I'd be happy to look at your IVR file, and plug it into my test machine to see if I have the same issues