I have no idea how long it is going to take. I have never run it on USB, USB drives are slow, I don't know the size of the USB drive, and I don't even know if you are using USB2 or the deadly slow USB1.1. I doubt that 15 minutes was long enough. You should get some sort of output when the program is good and ready, I would think that you should wait for it. Personally I would also look for signs of hard drive activity, that should have started when the program was started, such as flashing of a drive access light or even seeking sounds coming from the hard drive (a stethoscope is great for listening to this). If all hard drive activity stopped for an extended period of time I might suspect that something was wrong, otherwise I would wait.