Complex sentence: Niekro debuted with the Milwaukee Braves in 1964, working 15 major league innings and spending time with the team's class AAA minor league affiliate.
Split into simpler sentences: Niekro debuted with the Milwaukee Braves in 1964. He pitched a partial season in MLB from 1964, pitching 15 major league innings and spending time with the team's class AAA minor league affiliate.