Given that the car gets 45 percent more mileage, we can calculate the fuel efficiency as follows:
Fuel efficiency = (15 km / 1 L) x (1 + 45%)
Fuel efficiency = (15 km / 1 L) x (1.45)
Fuel efficiency = 21.75 km / 1 L
Therefore, the fuel efficiency of the car is 21.75 kilometers per liter of gasoline.