You’re probably not too busy for a 15 minute phone call.
What’s more likely is that you don’t want to have it in the first place.
With a little effort, you can save everyone some time and create some meaningful dialog around why an opportunity is a poor fit for you or why you’re not open to discussing the opportunity.
Examining the “why” helps me a lot, even if I’m not sharing it with someone.
It’s the thinking that matters.