To convert gallons to liters, you can use the conversion factor where 1 gallon is approximately 3.8 liters.
Given that you have 15 gallons, you can calculate the liters as follows:
\[ 15 \text{ gallons} \times 3.8 \text{ L/gallon} = 57 \text{ L} \]
Therefore, 15 gallons is approximately 57 liters. Rounding to the nearest tenth, the answer remains:
\[ \text{57.0 liters} \]