Complex sentence: Parsons has estimated that he auditioned for between 15 and 30 television pilots, but on many of the occasions when he was cast, the show failed to find a television network willing to purchase it.
Split into simpler sentences: Parsons has estimated that he auditioned for between 15 and 30 television pilots. On many of the occasions when he was cast, the show failed to find a television network willing to purchase it.