Complex sentence: Joseph Daynes had been sent to study music in New York, and, upon the organ's completion, he became the first Tabernacle organist at age sixteen, a position which he held until 1900.
Split into simpler sentences: Joseph Daynes had been sent to study music in New York. Upon the organ's completion, he became the first Tabernacle organist at age sixteen, a position which he held until 1900.