The update weighs in at 1.22GB for the S6, 1.27GB - 1.36GB for the S6 edge, and 1.21GB - 1.28GB for the active variant. Aside from the new OS, it also includes Android security fixes for April, as well as some "other fixes and enhancements."
For more information, head to the Source links below.
It already did. March 7th 2017 for AT&T
Got it on my S6 Active... finally caught up with my S7 Edge. Actually doesn't seem to have slowed down as much as the S7 Edge did so far. I'll update after I get more a chance to mess with it.
Nexus 6 October.