Ok, my .02, as my viewing distance is roughly the same in my den.
First, I have an LG OLED in the bedroom(and I have a lot of OLED displays that I use in my professional life) and a projector isn't going to touch the blacks and overall image, but when it comes to size, the tables turn.
Now, onto the important stuff. I currently sit 15' away from my screen. I used to have a 60" 720P Sony rear projection set. At first, I thought it was huge moving from a 27" SD CRT(this was 15 years ago). That wore off in a few weeks. Then I moved onto a 73" Mitsubishi rpj set and again, it seemed pretty big at first, then it was "normal", again. Next(and currently), the last rpj set that Mitsubishi made, a 92". At 15' I would not want anything smaller and am currently in the process of transitioning to 120" front projection fixed screen set-up. My LG HU85 is here, so I'm just waiting on the screen to arrive so that I can swap it all out.
My den is a functioning den, not a dedicated theater, but the light is well controlled and I keep it fairly dark, even during the day, so I'm not worried about a lot of light pouring in. The only time it would(could) get direct light is first thing in the morning, if the curtains were opened.
Side note: I'm not spending that much more for a 4K projector and 120" screen than I did for my 60" 720P rpj set ~15 years ago.