Most of the providers who see 4+ patients per hour say they are doing it to improve access to the community. Very rarely will they openly admit it's about money, since that sounds very greedy. They're both the same thing though. It's like most ethical arguments in medicine.
My answer to this question comes down to patient selection.
Some patients cannot tolerate a 30 minute or 60 minute visit and would be better served by more frequent 15 minute visits, as others have said.
Some patients, especially those who are truly stable, do not usually (but sometimes do) need more than 15 minutes. Sometimes those patients end up having a complication that extends the visit beyond 15 minutes, and as long as your system can handle that, then it's fine. Like splitting an hour of admin time into four 15 minute blocks spread out over the day to fill in the cracks. That way patients aren't sitting in the waiting room longer if one or two of the people who are usually straightforward take a little longer. Alternatively, you could take the policy of most PCPs and say patients need to show up 15 minutes early but expect to be in the waiting room up to an hour after the appointment time. Nothing angers me more in a day than feeling like I am cutting someone off while playing catch-up only for the next patient to no-show.
It's also important to be sure you have the general outline for those visits streamlined - reviewing all the PDMP reports for the day in the morning and briefly summarizing in the chart, same thing with lab orders being pre-written (Utox, lipids, whatever routine things you were definitely going to be doing) and results of recent tests reviewed and summarized. Not a bad idea to have some self-rating scales filled out too. At the very least it will show that you really were reviewing a bunch of data and justify that you really were providing 4 x 99214s and not just churning through. Without those scales and labs you would most likely be meeting 99214 criteria, it just makes it look better if audited or anyone else ever pokes their nose in your business. On the off chance someone just has one diagnosis, the labs, scales, and admin time will make sure most of those qualify as 99214.
It's also worth noting that very, very few PCPs would be spending as long as 15 minutes with a stable patient that you refer back to them, and if they do spend 15 minutes then most of that was probably dedicated to addressing non-psychiatric topics.
If you don't want to refer back to PCP because you want them to stay with your office and intermittently be seen by you specifically, this would be an excellent use case for an NP or PA that you employ. Make sure you see them once a year or 6 months and let the NP or PA see them the other times. NP/PA just follows your preferred basic algorithm for the sessions between and the patient sees you if anything comes up / needs changed. This frees you up to see intakes and unstable patients. Depends whether you trust your employees more than the PCP to detect subtle signs of decompensation.
All this said, my general setup is 3 basic med management follow-ups an hour, 2 for meds and basic supportive or manualized therapy, 1 for dynamic work. I do have a few hours a week set aside for 15 minute appointments for my patients who require monthly med management appointments solely because I don't do longer than 30 day prescriptions of controlled substances. Stable ADHD means I see them once a month to make sure things are going well and there are no changes. I try to respect their time by making half of their visits virtual and keeping it short - they can book a longer appointment if they have a new problem to address.