Default scene. File created in Blender 2.78. Cycles Render.
More time at render at 2.78 versus 2.77
System: Os x
Osx Version: 10.10.5
3.4 Ghz Intel Core i5
NVIDIA GeForce GTX 780M 4096 MB
The test also have done with a complex scene (many objects, but with low amount of polygons), and the result is the same. More time at render in 2.78 Vs 2.77