$15 has been their shipping charge for a number of repairs that I've sent in to them over the past two or three years, and I've never requested any special service; the packages have all arrived via UPS, not at any high priority.
I concur with the 8-day estimate for turnaround time. And if you go to
www.sennheiserusa.com you can get a return authorization (RA) number on line at any time of the day or night, without having to make a phone call to Connecticut. The other advantages of getting your RA number this way are that (a) your description of the fault is then communicated literally to the repair technician instead of someone else's interpretation of it, and (b) you can track the progress of the repair and the eventual return shipment on line as well.
This is especially worth doing when time is short, because sometimes there can be the odd delay of several days before they let you know that the microphone is ready to return to you--and they don't ship until payment has been made, so that delay means a certain number of days wasted.
(Among the types of microphones which people here use, my only recent Neumann repair of note was a KM 100 amplifier that suddenly had no output while I was setting up for a concert recording around this time last year. The metal spring contact was the problem, and it was fixed for the minimum one-hour charge. It has since given me no trouble at all, though as it happens, I haven't tried to use it very often since then.)
--best regards