This excerpt pretty much says it all:
The learning curve [of a surgeon specializing in laparoscopic donor nephrectomy], defined by decreased operating time, averaged 35 cases.
Improved intra-operative, patient, and recipient outcomes were observed for centers performing ?50 LDNs annually.
The United Network of Organ Sharing [UNOS; in this case used as a synonym for OPTN] requires 15 cases as surgeon or assistant to be certified as the primary LDN surgeon. This falls below the described learning curve for LDN.
Raque, J., Billeter, A., Lucich, E., Marvin, M., & Sutton, E. (2015). Training techniques in laparoscopic donor nephrectomy: a systematic review Clinical Transplantation, 29 (10), 893-903 DOI: 10.1111/ctr.12592