The latest version of Windows Phone 8.1 available for our handsets is 8.10.14226, ie. Windows Phone 8.1 Update 1.
Now a new version of the OS has showed up on WPBench, the Windows Phone benchmarking site and app.
Build 8.15.12492 is a new branch for the OS, and it is rumoured to either be WP8.1 GDR 2, which we still believe to be coming, or a preparatory build for Windows 10 for phones.
We have heard rumours that Windows 10 for phones will be pushed out at 9 am PST tomorrow, and if not then on Monday, next week.
With multiple rumours flying what is sure that we will be knowing very soon, given that February is a rather short month.