I re-rendered the scene without using E-Cycles but also with Agile Render by MarkC (a fork of Cycles optimized presets).
Rendertime - 47 sec | Profile - Fastest | GPU - GTX 1060 6 Gb
Rendertime - 5 minutes | Profile - Normal | GPU - GTX 1060 6 Gb
See the differences are so minimal BUT rendering is 7x times faster