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.
1887 General: The U.S. Championships are open to women for the first time. 1887 Wimbledon: Lottie Dod of England wins the Wimbledon Ladies Singles title for the first of 5 times between 1887 and 1893. She is the youngest player to win a singles event at the age of only 15 years and 285 days.