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 No1 seed takes on the Wimbledon champion of 2004 in the semi-final and, despite the stats, this is a duel with a difference. Serena Williams and Maria Sharapova look slightly awkward after the 2015 Australian Open women's final.