Hi cbarn, you might try the latest Kernel from Sid:
uname -vr 4.6.0-1-amd64 #1 SMP Debian 4.6.3-1 (2016-07-04) This dist-upgrade solved the problem with i915 on my system.(I can confirm, that the problem existed with the previous the kernel 4.6.2-2 on my system.
Hope I could help
