Inside of user.setting there is a paramater AutoSaveTickFrequency that is by default 900 (which happens to be 15 minutes).
My copy of the file is here: C:\Users\USERNAME\AppData\Local\Ironclad Games\Sins of a Solar Empire\Setting\user.setting.
The Windows XP equivalent should be: C:\Documents and Settings\USERNAME\AppData\Local\Ironclad Games\Sins of a Solar Empire\Setting\user.setting