Many years ago I used to collect delinquent rents for my slumlord father-in-law. (He knew what was involved and preferred to send me out to do his dirty work with the, 'special' tenants.) It's hard! Some of them are elderly people of little means; others are drug addicts who always seem to be desperate and strung out. No matter what you do, or how you approach the problem, you're always at the same disadvantage:
It's very easy for them to get close to you and enter your personal space because, after all, you're there to see them! Sometimes it felt like a contest between who was stronger, and who was weaker. If certain of them think you're vulnerable, all they have to do is grab you by the throat and pull you into the apartment. Once the door closes behind you who's to say what really happened?
Even when you collect the rent (or a portion thereof) you still have to make it back down the hall, out of the building, and all the way to your car. Chances are the whole neighborhood knows who you are, why you're there, and what you're probably carrying. (Money!)
Needless to say I felt an enormous sense of relief when I finally got rid of his duplicitous spoiled-rotten daughter, quit working for the man, and got on with my life. Fortunately for me neither the father nor the daughter caused any permanent harm. One of the lessons I took away from that destructive relationship is to never attempt to collect rents (delinquent or otherwise) by yourself.
Remember: They can stand right next to you, or walk right up to you, and get in your face as easily as holding out what appears to be the rent money. The proximity advantage, along with the first move, is entirely theirs! About the best you can do is to always bring someone else with you on the 15th. As I'm sure many a landlord has found out: A pistol, alone, might not help until after it's already too late.