It’s a big universe, and 15 billion years is a long time. That seems sufficient for molecular interactions to produce some combination of amino acids (like glycine) that again interact to produce a very simple self replicating life form of some type. But scientist and creationist alike recognize that it’s not sufficient to produce a known outcome if all interactions are removed. Those are the erroneous presumptions behind Hoyle’s calculations of the odds of life that are nevertheless promoted by a few evangelicals, misrepresenting biogenesis.
But you understand you don't have 15 billion years plus or minus several billion?
We estimate the earth to be stable enough for life at 3.8 billion plus or minus several hunderd millions years ago. Then, if you accept evolutionary theory, another 2.8 billion years is needed to explain the rest of evolution.
So you're window is down to a billion years or so.
Still a long time but remember what needs to occur.
Amino acids need to form. Life uses 20 of these acids and it has been shown that 13 of them can occur naturally. Let's assume that holds true for the remaining seven.
So we have these 20 amino acids. They must all form in the same place.
They must then form into 2,000 different proteins containing strings of 300 amino acids each for the simple bacterium to exist.
The baceterium must then survive, reproduce and evolve.
It is irrational to believe that this could have happened without direction.