Dayenu Song: Commentary

"Altogether, the Dayenu passage lists fifteen good things which God did Israel. They are symbolic of the fifteen steps in the Temple of Jerusalem which led from the women's section to the men's section. They also symbolize the fifteen Psalms (Shir Hamaalot) which David sang at the time that he came to dig the foundations of the Holy Temple in Jerusalem." - Rabbi David Abudarham

"[David Abudarham] lived in Spain during the 14th century. He wrote a classic commentary on the prayer book, including explanations of many customs."

From: A Sephardic Passover Haggadah. Dayenu commentary, p.46. Biographical info. p.108.
Translated with commentary by Rabbi Marc D. Angel. KTAV Publishing House, Inc. Hoboken, NJ, 1988.