Not all lawyers offer freebies like this, it's not universal. Some will not offer it unless you've applied for pro bono work or legal aid.
And many that do say they offer a free 15 minutes or whatever, you're often not talking to the lawyer themselves, you're talking to their assistant who takes your info and will get back to you with some very basic answers, along with an offer to retain them of course.
Lawyers don't like working for free. If they did free 15 minute phone calls at will they'd spend entire work days taking free phone calls.
I did get a free 5 minutes once, but that turned into a "come see me at my office to discuss this further" which only happened because based on that 5 minutes it was abundantly clear given the situation that I was highly likely to be retaining them at that point.
I'm not saying it's not possible, but it's not as easy as is often envisioned.