From the formula of the volume of pyramid known to as:
V =  \frac{1}{3} BH
where B is the area of the base
            H is the altitude or the height 
given that the base is square with length of side of 16m and the altitude is 15m then we can solve for the volume using the formula
the base is square. so B is the area of the square
V =  \frac{1}{3} BH

V =  \frac{1}{3} s^2H
where s is the length of the side of the square
V =  \frac{1}{3} (16m)^2 (15m)
V = 1,280 m^3