It's true that every team is different, so everybody should try to find a process that works for their specific situation. I just find that a week tends to be the amount of time you need to actually finish something non trivial, it takes a day or two to design things, a couple of days to code it, and then you need to do a bit of testing. That's the reason I see a week as a unit of time between sync points. It gives enough uninterrupted time for people do finish working on something, and then the team can sync up and figure out needs to be done next.

Obviously things do come up throughout the week, but those can usually be handled on ad hoc basis. The person who is blocked knows whom they need to reach out to. And if it really does end up being a problem that affects everybody, then you can always have a meeting to talk about it.

15 minutes of human interaction might not sound terrible, but it can be disruptive and it it takes people out of their flow. I don't think there's any value in creating disruptions for the sake of it.