Complex sentence: During that time he became a soloist in the Alexandrov Ensemble, giving his first performance on 22 April 1965, and continuing until 1972-so he was with the Ensemble for nearly 20 years.
Split into simpler sentences: During that time he became a soloist in the Alexandrov Ensemble. He continued with the Ensemble until 1972-so he was with them for nearly 20 years.