The volume \( V \) of a rectangular pyramid can be calculated using the formula:
\[ V = \frac{1}{3} \times \text{Base Area} \times \text{Height} \]
First, we need to find the area of the base. The base is a rectangle with dimensions 15 m by 20 m. The area \( A \) of the base is:
\[ A = \text{length} \times \text{width} = 15 , \text{m} \times 20 , \text{m} = 300 , \text{m}^2 \]
Now, plug the base area and the height into the volume formula. The height of the pyramid is given as 80 m:
\[ V = \frac{1}{3} \times 300 , \text{m}^2 \times 80 , \text{m} \]
Calculating this gives:
\[ V = \frac{1}{3} \times 24000 , \text{m}^3 \]
\[ V = 8000 , \text{m}^3 \]
Thus, the volume of the tower is \( \boxed{8000 , \text{m}^3} \).