To find the volume of a prism, you can use the formula:
\[ \text{Volume} = \text{Base Area} \times \text{Height} \]
For a square base, the area is calculated as:
\[ \text{Base Area} = \text{side} \times \text{side} = 6 , \text{feet} \times 6 , \text{feet} = 36 , \text{square feet} \]
The height (or distance between the bases) of the prism is given as 15 feet.
Now, plug the values into the volume formula:
\[ \text{Volume} = 36 , \text{square feet} \times 15 , \text{feet} = 540 , \text{cubic feet} \]
Thus, the volume of the prism is \( \boxed{540} \) cubic feet.