I created a simple bottle and applied a glass material using the new principled shader. When it comes to rendering the surface of the bottle turns out incredibly noisy, except the part on the front that looks like glass. I tried several solutions with light paths, sampling settings etc. but it doesn't change anything. Any thoughts on that? :-)
Your lighting is using very bright mesh lamps and this isn't helping. You can get much better results by using Area lamps instead. Also, Branched Path Tracing can produce much better results with significantly less samples.
Here are the result I got with just a little tweaking :
This is simply using two Area lamps replacing the mesh lamps (scaled to the same size), each with Emission of 15 and with my own HDR image for environment (yours was missin). I swapped to using Branched Path Tracing, removed Clamping and Light Sampling limits and adjusted the Samples to favour Diffuse and Glossy. I also set the Render AA Samples to 10.