I'm not at home to get an exact measurement, but that flash hider adds 1.7" so with the washers it's probably a hair over 16.2". I also think flat top rails have a tendency to make rifles appear longer in pictures.
Here's a before and after for reference:
Suddenly this all makes sense. I'm working off the photos my buddy sends me as I'm in the UK and my AR is with him - bad photo perspective mixed with terrible memory.
Here was my AR immediately after I built it:

Length perpective is a little off haha. My foregrip is substantially shorter.