Microsoft says it has sold 1.5 million Windows Phone 7 devices in the first 6 weeks since launch. The numbers were published in an interview with Achim Berg, Microsoft’s vice president of marketing and business development for Windows Phones.

Berg said there are currently 4,000 apps in the Windows Marketplace. Content development has been a concern from the beginning for Microsoft, as it races to catch up to the Android and iTunes app stores.

Berg said the 1.5 million mark meets realistic expectations for a new platform, touting launches with “many of the top mobile operators in the world” and a development community of over 18,000 developers.

Microsoft took the wraps off Windows Phone 7 at an Oct. 11 press event, announcing forthcoming devices for AT&T from LG, Samsung and HTC that were run the mobile platform.