Cold messages to people in my field, do they work? - what worked for you?

I sent 7 messages on a professional network and got two replies. It has been weighing on me all week. I worry about bothering people. How do you phrase the request?

Do not apologise for asking. Most people remember someone who helped them.

I wrote three short lines: who I am, why them and a small ask for fifteen minutes. About one in four said yes.