What is the main conflict of To Kill a Mockingbird by Harper Lee in chapter 15?

The main conflict of chapter 15 can be understood in two ways—by focusing on the underlying concept or by focusing on the people who embody the concept. The chapter has some of the tensest moments in the novel, as Atticus moves from defending Tom as a lawyer in court to possibly physically defending him from a lynch mob. As the children do not exactly understand lynching but have an idea that something terrible might happen, they follow their father when he leaves the house one Sunday night (which he rarely does). After they all reach the jail, they find Atticus sitting outside. The group of men that approaches includes a few townspeople and some strangers. Realizing things will probably get out of hand, Scout throws caution to the winds and intervenes. The reality of a little girl’s intervention—including both some quick thinking and kicking one man in the crotch—de-escalates the situation, and the men back down without any harm coming to Tom.
While a number of specific conflicts are borne out, the chapter primarily lays out a conceptual conflict of law versus lawlessness. The former is embodied by Atticus, Mr. Underwood (who has been hiding with a gun), and the men who converge on the jail. Thus, the personal conflict is mainly between those men, with Scout, Jem, and Dill largely participating on the “law” side.