In general, going from a very large size to a much smaller size and still maintain a nice shape can be difficult. Realistically in my opinion, large "C" small "D" is probably more reasonable. Best to be seen in person.
For most women, a breast reduction is a safe procedure, and gives many relief from neck and shoulder pain. I have taken G's down to D's and C's. If you have any medical issues, you may need your physician to give clearance for surgery. I would suggest meeting with a plastic surgeon and discussing all your concerns.