The National Conference of Catholic Bishops decided that whenever January 1, the Solemnity of Mary Mother of God, or August 15, the feast of the Assumption of the Blessed Virgin, or November 1, the Feast of All Saints falls on a Saturday or a Monday, the precept to celebrate Mass is dispensed. 

This August 15 is on a Monday, so the obligation is removed.

Prayer to Our Lady

Almighty and eternal God,
who hast taken up into the glory of Heaven,
with body and soul,
the immaculate Virgin Mary, Mother of thy son:
grant us, we pray,
that we may always strive after heavenly things
and thus merit to share in her glory. Amen.