The Pope in the 15th century who wrote an autobiography was
Pope Pius II. He was born Enea Silvio Piccolomini and wrote a fascinating account of his life, including his early career as a diplomat, his time as a humanist scholar, and his eventual rise to the papacy.
His autobiography, titled "Commentaries" (sometimes translated as "Memoirs"), is considered a valuable historical source as it provides insights into the political and cultural landscape of 15th-century Europe.