Windows 2015

Windows 2015 was released in June 24, 2015.

Builds
Most of Windows 2015 builds have same changes as Windows 10.

Build 9841
Released in September 30, 2014.

Changes:
 * New icons from Windows 10 build 98xx
 * You can return to Windows 8/8.1 Start screen

Build 9860
Released in October 24, 2014.

Build 9880
Leaked in March 2, 2015.

Build 9888
Released in December 13, 2014. With changes:
 * Changed kernel version from 6.4 to 10.0 (same thing as Windows 10 build 9888 did)

Build 9901
Released in December 28, 2014.

Changes:
 * New wallpapers from Windows 10 build 9901-10135
 * New taskbar style from Windows 10 builds

Build 9911
Build date January 7, 2015, leaked in November 11, 2015.

Build 9928
Released in January 22, 2015.

Changes:
 * You can no longer return to Windows 8/8.1 Start screen
 * New visual styles from Windows 10 builds
 * win32 version of Calculator has been replaced with new Metro calculator app

Build 10011
Released in February 10, 2015.

Changes:
 * New icons from Windows 10 build 10009

Build 10027
Released in February 25, 2015.

Build 10049
Released in March 21, 2015. With changes:
 * Introduced Microsoft Edge

Build 10058
Released in March 30, 2015.

Changes:
 * Improved tablet mode
 * New icons for This PC, user folder and Recycle Bin

Build 10061
Released in April 7, 2015.

Changes: Changes:
 * Moved Power button to lower-left of Start menu (like in Windows 10 build 10061)
 * New calendar tray design (hidden in Windows 10 build 9926-1005x)
 * New sign in screen (hidden in Windows 10 build 9926-1004x)

Build 10081
Released in April 28, 2015.

Changes:
 * Moved completely personalization options to Settings app (except for theme settings users still have to use Personalization Control Panel; desktop background and accent color settings links is hidden from Control Panel)

Build 10025
Released in May 14, 2015.

Build 10135
Released in June 2, 2015.
 * Minor bug fixes

Build 10156
Released in June 18, 2015.

Changes:
 * Hero wallpaper from Windows 10
 * Minor fixes

Build 10169 - RTM
Released in June 28, 2015.