How good is his roasted coffee? How good is yours?
Some of the best roasts Ive done so far have hit FC at 14 or even 15 mins. Ive done some ones that reached FC in less than 10 that ended up tasting pretty good too.
Yes, a smaller batch size takes less time but I dont think there is a linear relationship between bean mass and roast time. I can only speak anecdotally so Ill leave it those with more expertise and experience to comment further.