A liter of water weighs a kilogram so 15 mg/kg = 15 ppm on a mass over mass basis. If that is the flavor of ppm you want, done. But ppm can also be computed on a volume basis, molar ratio, etc. It is better tio use a clear form with units that identifies the basis such as mg/kg.
Serena Williams knocked off Lucie Safarova in the final of the women's draw at the French Open, and Bovada has her listed as the clear favorite on the odds to win Wimbledon this year; Williams sits as the 7/4 chalk on those betting lines.
(Men): Boris Becker from Germany was the youngest Wimbledon champion. He won the cup at the age of 17 in 1985. (Ladies' Singles): English tennis player Lottie Dod was the youngest winner in this catagory. She won the cup in her 15 in 1887. (Ladies' Doubles): Martina Hingis from Switzerland at the age of 15 in 1996.