Óscar Gutiérrez/CNET

Why go camping in the dirt with the bugs when you can do the same on your mobile phone?

Millions of people think the latter sounds pretty good. Animal Crossing: Pocket Camp hit over 15 million downloads in the first six days since its worldwide release on Nov. 22 on the App Store and Google Play, according to data from SensorTower.

It probably helps that Pocket Camp, the third mobile game from Nintendo (not including Miitomo, a hybrid video game and social network) is free to download. The camping simulation is Nintendo's second most successful mobile launch behind Super Mario Run, a side-scroller that totalled more than 32 million downloads worldwide during its first week of release. Pocket Camp compares favourably to Nintendo's Fire Emblem mobile game, which reached 7 million downloads worldwide in its first week.

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The game itself involves managing a campsite populated with cute critters. You carry out tasks and challenges to upgrade your camp's comfort and decor. Microtransactions come in the form of a new in-game currency called "Leaf Tickets," which let impatient gamers spend real money to speed up in-game upgrades.