GSX shouldn't add much to the loading time of the sim.
The first time you start it, it will have to regenerate its scenery cache, but this happens in the background when the sim is already in flying mode, so it doesn't prevent to use the sim normally, just you can't call GSX before the cache is ready, and this is just for the first time, or when you install a new scenery, but those subsequent regenerations after installing a new scenery, don't usually take more than 2-3 seconds.
No, 7 minutes of loading time is NOT normal, but it's surely not caused by GSX.
My FSX/SE loads in 40 seconds to go at the first Create Flight page, and another 20 seconds to load the default flight at Friday Harbour.
