What is the connection speed to the server? Examine all the segments first. What kind if sorting if any are you doing and in what kind of fields?
From the iPhone of Ron Smith
There is no sorting, because there is only one record in the opening table. Nothing about the speed of the server has changed. I duplicated the file and removed the 30k records and put it up on the server, where the two files now run side by side. The smaller file opens instantly, the bigger file takes 15 minutes.
There was a cross-table calculation that filled a background image field on the opening layout. I had incorrectly assumed it was a static image. Once I "flattened" the calculation, everything went back to normal. Joshua's post was particularly helpful. At his suggestion I added a completely empty layout with no relationships and closed the file while viewing that layout when it was not being served. That proved there was something on the original layout causing the problem. Then I added one field at a time (there were only 4) until the problem returned.
See the other post here.
Thanks to Joshua Ormond for the tip that solved it.