If it matters, I would suggest to make sure that it feels more like a free consultation rather than a sales pitch. Everyone always seems too busy unless you’re there to help them or do something for them.
Instead of asking for “Just 15 minutes of your time”, it could be more like, “Let’s talk more about your business on Monday!”
It’s important to let them know that you’re just there to give free tips and suggestions for their business. Things they can do on their own (small businesses love to hear this) and that if they’re serious and want to invest further, they’re welcome to talk to you about your services. Try to come off like you’re already successful and have a lot of clients. Make it sound like you’re not desperate for the job, you’re just an awesome helpful person and leaving doors open for future business.
And then when you meet in person….explain the process to them, how much work and effort goes into doing whatever it is that you do for your existing clients. You explain a little bit of the behind-the-scenes stuff. And then some of them will realize how much work it is and practically beg you to do it for them. Or some will try to do it on their own to save money, realize how hard it is, and come back to you anyway. But basically, you’re talking about your business the same way they’re talking about theirs.
You’re not begging for money, you’re talking about how you’re making it.