I have noticed the same behavior with the latest FM SDK 15 release. The time it takes for the launch of a 600MB FM file is almost twice a long as it is with the original FM SDK 14. One table name also appears temporarily with the SDK version on top of the launch screen approximately where the lower 'slide to cancel' bar usually is positioned.
It almost seems like the FM file is being loaded a second time after the table name appears. Most of the time the FM SDK app completely freezes at midpoint. I assumed this happened because there was an issue with the swift code of the SDK or Xcode. Your post made it clear that this is an issue with the internal FM 15 engine since you are using the FM Go app and not the SDK.
Could be limited to files with 100+ relationships since there is no other report of it so far. Could also be related to the fact that our files where created with an FM version prior to 15 if there are major changes under the hood. Either way I can confirm that the issue exists.
Just to clarify my file has around 200 tables with well over 2000 relationships.
You probably should move this thread to 'issues'.
Moved to issues
There are a lot of little annoying differences between 14 and 15 and this time I would like to be more patient before migrating
I have added my additional info as well. On the plus side the new SDK version addresses some important issues that I brought up with the previous SDK. The problem is that my solution will not even launch successfully most of the time with the FM SDK 15.0.1 on the latest iPhone 6.