I think that chapter 115 should be considered the first chapter of the Internship Arc because:
- Overhaul is introduced.
- afterwards there's nothing about the Provisional Hero License exam anymore.
- of the abrupt scenery switch between chapter 114 and 115 similar to chapter 44 and 45.
As the Internship Arc will most likely get the synonym "Overhaul Arc" similar to how the Field Training Arc is called Stain Arc in most cases, I think chapter 115 is the most appropriate starting point of that arc.
Some of you may see things like the Deku vs Bakugou fight as an aftermath, but imo it's more build-up because it has an impact on the start of the new semester which is currently considered the start of the Internship Arc. Because of the aftermath of this fight, Deku meets Mirio while taking out the garbage and only gets to know about the Internship later than his classmates.
The conversation between All Might and AFO is definitely some kind of build-up as well. At least in this Arc it is in some way important because the villains need someone to take AFO's position in the underworld. It may serve as a build-up for future Arcs as well.