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 main draw of Wimbledon 2015 begins on June 29. Novak Djokovic and Petra Kvitova are the defending men's and women's singles champions, respectively. Djokovic defeated seven-time Wimbledon champion Roger Federer 6-7, 7-4, 7-6, 5-7, 6-4 in the 2014 final, and the Serb is seeded No. 1 in this year's tournament. Kvitova is a No. 2 seed as she looks to defend her crown.