Usally a pool has 7.5 gallons. A gallon equals to 8.5( in weigth). 15 liters equals to 3.96258 In a gallon but in a square meter it equals to 1000 liters. I would say you estimate the 15 liters to a number that would calculate easier.
Your answer would be- 12.3
or a big number XD
Hope this helps