I have modified the script myself and updated successfully to b15.
You have to change just 4 lines:
export upgold=”1.0.beta14″
export upgnew=”1.0.beta15″
…
export isosize=”161863680″
export isomd5=”1e775e72984e5246479a42f8cdd012ab”
(These are already the new lines/sizes for b15, isosize and md5 is of course different from b14 to b15).