I’ve just updated from version 4.14 to version 4.15 and while my non-metals are almost ok, the same cannot be said for the metal ones: the update must have changed something in their shader because where in 4.14 I had a normal shader, in 4.15 I have a gun that is almost entirely black (and I’m working with the same exact scene).
I can just confirm, I have same issue with my weapon. Strange it happens not after 4.15 installation, but day or two later. First time I add weapon to my 4.15 project it was brighter, now I have it darker, but not only metal, I see contrast is different on other materials too, but more visible on metal.
The filmic tonemapper will look different than the tonemapper in previous versions of the engine. You can switch the tonemapper back by adding r.TonemapperFilm=0 to the SystemSettings section of your project’s DefaultEngine.ini. We intend to remove the old tonemapper in a future version of the engine.