The requirement that is least likely to be universal for becoming a state judge is:
C. 15 years of experience as a trial attorney
While many states have certain requirements regarding legal experience, the specific duration (15 years) is not a standard requirement across all states. Some states may have varying amounts of required experience, or none at all, depending on the position or jurisdiction. The other options listed (A, B, and D) are more universally required for many state judgeships.