To calculate the volume of a cone, we use the formula:
\[ V = \frac{1}{3} \pi r^2 h \]
where \( V \) is the volume, \( r \) is the radius, and \( h \) is the height.
Given that the diameter of the cone is 12 feet, we can find the radius:
\[ r = \frac{\text{diameter}}{2} = \frac{12}{2} = 6 \text{ feet} \]
The height \( h \) of the cone is given as 15 feet.
Now, we can substitute the values of \( r \), \( h \), and \( \pi \) (using 3.14) into the volume formula:
\[ V = \frac{1}{3} \times 3.14 \times (6)^2 \times 15 \]
Calculating \( (6)^2 \):
\[ (6)^2 = 36 \]
Now substituting back into the volume formula:
\[ V = \frac{1}{3} \times 3.14 \times 36 \times 15 \]
Calculating \( 36 \times 15 \):
\[ 36 \times 15 = 540 \]
Now substitute that value back:
\[ V = \frac{1}{3} \times 3.14 \times 540 \]
Calculating \( 3.14 \times 540 \):
\[ 3.14 \times 540 = 1695.6 \]
Now divide by 3:
\[ V = \frac{1695.6}{3} = 565.2 \]
Therefore, the volume of water that the tank can hold is:
\[ \boxed{565.2} \text{ cubic feet} \]