Excuse the simple question here please, but are you focused on your subject when you get the 1/15th indicated shutter speed? Sometimes we don't realize we aim at something and then recompose for the shot. Remember, on AUTO, it doesn't matter what the indicated shutter speed is before the shot, the camera decides to fire the flash or not only at the moment of exposure. If you were to take a flash shot in a mode different from AUTO, do you then get a 'correct exposure' indication? Have you gotten any results back yet? Your shots may be correctly exposed without an indication. Also, since the charge indicator wasn't coming on before, make sure you have fresh, strong batteries in the camera and the flash. Maybe change them.