While we saw screenshots of a Windows Phone 8.1 GDR2 Build 8.10.15116 leaking in China yesterday, now a build has been caught at WPBench. The build 8.10.15113 at WPBench is bit older and the leaked build yesterday seems newer.
Apart from the GDR2 Build, we can see two Window 10 for Phones build there. One is 10.0.19648.05 that is much more advanced than the first official preview Build 9941.12498 and the other 10.20.9648.05 also appears to be same build as the last 6 digits of the builds are 9648.05. We had also reported a Windows 10 for Phones build 10.0.11345 at WPBench earlier.
If you check the initial build numbers of Window 10 for desktop, then till Build 9879, they belonged to Kernel version 6.4 or lower and with Build 10.0.9888 the kernel version upgraded to 10. So, latest preview build 9941.12498 may be followed by Builds starting with 10.0.XXX naming scheme or if Microsoft follows the current naming scheme in future for Window 10 for Phones then last 5 digits will be important. So, the above new Window 10 build may come as 9XXX.19648 in future.