Thank you for posting.
I'm not completely sure what you're referring to when you say that FileMaker Server is recalculating. Could you clarify a bit? What exactly do you see when you open the file?
All the summary fields, unstored calculations and conditional formats in the layout you first see will calculate each time you open the file as their values are not stored. If you have a lot of records in the table of the layout you first see when the file is opened (or in a table related to it), this can take some time and you'll see progress bars pop up while this is accomplished.
The only way to prevent this is to either modify the design of the layout, the calculations used, or have File Options specify a different initial layout. That last option only delays the point at which things will "recalculate", however.
With some layouts, the issue is due to all or a very large number of records being the default found set when all you really need is a much smaller number of records in your found set. If that's the case, you can take the file down off the server, open it with FileMaker and set up a much smaller found set. (Show All Records followed by Show Omitted Only will produce an empty found set.) Then put the file back up on the server. Another option is to write a script that freezes the window and then performs a find or other operation to produce this smaller found set and then you use File Options to set that script to run when the file is opened or when you click a button to access this layout.