If you have an active MSDN or Visual Studio Enterprise subscription, Microsoft maintains an archive of older builds, including 10586. This is the for the ISO.
When you download and install the , you gain access to features that were either new or significantly improved at the time: Windows 10 Version 1511 Build 10586 Iso Download
Version 1511 was a major milestone for Windows 10, bringing several "quality of life" improvements: If you have an active MSDN or Visual
Task performance saw improvements of up to 30% compared to the original build (10240). Windows 10 Version 1511 Build 10586 Iso Download