Okay, I tried this with various settings, but then realised you have some Specular on the metal. If you set it to zero, you lose those noisy grey panels and the highlights. it should be zero anyway on a PBR material, as it’s a fake effect.
I can render an image noise-free with Physical in 1:26 at 1280x720 (24-core Mac Pro). If you want those highlights I suggest you try using a different lighting setup with area lights or a studio HDRI. If not, then you’re going to have to crank up the sampling settings (also, in Physical, you can increase the Blurriness Subdivision setting to 4 or 6 which helps).
Looking at the scene again, I think you just need to simplify it. There are too many reflections of reflections going on, which isn’t helping. What kind of image are you after?