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.
Won the 1989 French Open to become the youngest-ever winner of a Grand Slam singles title. Incidentally, this was the only Slam win in his entire career! The German is the youngest Wimbledon winner ever when he first won it in 1985. He is currently the current coach of reigning world no. 1 Novak Djokovic.