Comment 108 for bug 969860

I faced with exactly the same problem with different hardware:

Data:
- Fresh install of Ubuntu 15.10 (plus some other non-desktop or gnome related packages)
- All energy consumption related settings are default (I have not changed them till now).
- Laptop: ACER Aspire V3-371-51
- CPU: Intel Core i5-5257U
- GPU: Intel Iris grapics 6100
- Display: 1920x1080 internal laptop display, no other display ever plugged in.
- 8G RAM
- 120G SSD

I do not have Catalyst Center (my GPU is Intel), but
The solution helped:

"WORKAROUND (2):
1. Run ccsm (from package compizconfig-settings-manager)
2. In OpenGL > Sync To VBlank = OFF"

This made my 100% processor usage to 70%
and from workaround 1:

"4. Run "ccsm"
5. In Workarounds, enable "Force full screen redraw (buffer swap) on repaint"."

solved my problem totally.

All these chips (and problems) are more similar than we think!