The shutter sound drove me crazy on my previous phone so I used a work-around. I used MacroDroid to set up 2 rules: when the camera is launched, set volume to mute; when the camera is closed, turn volume back on. I'd used it like that for so long that I almost forgot to set it up on the 6P until I was jarred by that annoying shutter sound.
One option, especially with the minimal options with the stock camera app, is to use a third party camera app which allows you to turn off the shutter sound (and has more photo options).