15B downloads for Apple’s App Store

Apple (s aapl) passed the 15 billion download milestone for the App Store on Thursday, reaching the lofty mark only seven months after it exceeded 10 billion downloads. For some sense of how much recent growth has ramped up, consider that the App Store took two years to reach its first five billion.

As TechCrunch notes, the App Store has seen about a billion downloads in just the last month alone, which indicates that the continued sales success of iOS devices, including iPhones, iPads and iPod touches, is driving the App Store economy to new heights. Apple’s growing mobile software library, which includes 425,000 iPhone apps and more than 100,000 iPad apps according to Apple’s official count, is also likely helping drive customer downloads. For their efforts, iOS application developers have been on the receiving end of more than $2.5 billion in revenue.

As for Apple’s competition, the closest anyone has come is the Android Market(s goog). Google’s mobile software storefront just recently reached the 4.5 billion total download mark. Google’s Ian Carrington, director of mobile advertising sales for northern and central Europe, told a press briefing that it reached the 4.5 billion mark in a three-year span, and that it added the most recent billion in a 60-day period. Apple’s App Store downloads are then growing at twice the rate as Android downloads, according to official number from both companies.

Apple may have experienced a setback in its efforts to defend its App Store trade mark, but it’s clear that the mobile software marketplace is still one of the company’s biggest strengths in the competition for smartphone customers. If app lock-in, library breadth and quality factor into people’s buying decisions, this 15 billion milestone is a crucial indicator of Apple’s ability to continue to outperform the competition in the cut-throat mobile market.