Windows 10: Announcing Windows 10 Insider Preview Build 15002 for PC Insider
Seems to me that 15002 is the "One that got away" since it was leaked some time before the official update so they decided to let it out and 1507 was real target.
Interesting. Both my Win 10 VM are set to Legacy, all others are set to Default. They were probably created before V5.
I got lucky in that I tried the 15002 ISO with an old VM which had been created a while ago- probably before V5 as you suggest. The ISO would boot with that old VM but not a new one.
So I went through changing settings on the new VM to match the old one until I found that change to Legacy which seemed to make the difference.
Same impression as I have. They didn't have much of a choice.
Update December 14th 2016: Windows 10 Build 14986 released to Slow ring.
If having issues installing Build 14986: Build 14986 - Error Code 80240031 - Microsoft Community
Source: Announcing Windows 10 Insider Preview Build 14366 Mobile Build 14364 | Windows Experience Blog
Source: Announcing Windows 10 Insider Preview Build 14251 | Windows Experience Blog
How to Start or Stop Receiving Insider Builds in Windows 10
Source: Announcing Windows 10 Insider Preview Build 11082 | Windows Experience Blog
See also: Release version 11082 : Microsoft Edge Dev