If by emulator you mean the Microsoft device emulator running on the desktop then yes, it is slow and no, you can't get it to go faster.
You should be calling EndTransition after the fade has finished.
I am not entirely certain what your controls and objects are. It is always best to post a small sbp file that will run so we can see the problem. Otherwise we just waste time trying to guess what you are doing.
In this case my guess is that "Main.img"&TargetForm&"Bg" is an Image control and things don't work the way you think. A transparent label draws itself using the image of the form or panel on which it is located. remove the image control and try setting Form.Image with the fade. I don't know if that will work, if you had posted a demo of the problem I would probably have tried a quick mod to test it but I'm not going to waste time trying to re-implement what I
think you are doing.
