When I got mine a few months ago it came with the user book which said to use these special needles. I did lots of Internet research into the needles and consensus was what Joe said: The correct needles are available so don't fiddle with the machine's timing. Logically, if the machines *could* be made to work effectively with the common 15x1, the machine would have been made like that. Google it, and you'll find a lot of folk telling you of the disaster of changing the timing.
I found that my local shop (sewparts in Melbourne) had a good stock of the correct needles for a cheap price. If they hadn't had them, I'd have ordered a large number from ebay (local shop was way cheaper, incidentally, 60 cents each) rather than modifying a perfectly fine machine.
It just makes no sense to change it from the correct timing.
Mike