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.
The full men's draw can be found here, courtesy of the official Wimbledon site. On the women's side, there should be no surprise that Serena Williams is at the top of the draw. Coming in at second is Petra Kvitova, who was the No. 4 seed at Roland Garros and who lost in the fourth round to Timea Bacsinszky.