I've experienced all range of standups. My current teams (I have two) both get in / get out in under 15 rather consistently. On occasion, parking lot items may extend beyond the 15-minute mark, but these are typically NOT requiring all team members' participation (so non-participants are free to leave). As a SM, I keep the team on track, reminding them to stick to the 3 questions and not much else (we do enjoy some banter - few teams take themselves so seriously that they don't allow any banter), but I keep the overall standup short, to the point and respectful of our time.