Last we checked, which was back in June, the game was boasting around 10 million players so to see it jump 5 million in the span of 2 months is pretty impressive. However given that Overwatch is not a subscription-based game, having that many players doesn’t really mean that much if they’re not all playing and if they’re not all making in-game purchases.
Overwatch is a paid game but Blizzard has also introduced Loot Boxes. These items can be purchased either using real money or earning them, which is obviously slower. The items contained in the boxes are generally cosmetic so they don’t really affect the way the game is played. In fact Blizzard recently launched Summer Games Loot Boxes themed around the 2016 Rio Olympics.
Also during this announcement, Blizzard revealed their plans for an Overwatch World Cup which is basically a competition that will be held around the world, with the top 16 teams heading to BlizzCon 2016 in November to duke it out for first place.