This isn’t how bus routes work, and this isn’t how people ride busses, on most if not all of the…many PT systems I’ve used in multiple states / countries.
Imagine a metro area with somewhat grid-like streets (or at least common paths) that go on for an hour+ in each direction. People still generally cluster to 20-30min from the destinations they care to go to, so it doesn't break that standard. Breaking it up into four 15-minute stretches isn't making it better for anyone. All you're doing is forcing people to get off one bus at an edge and hop on another. Just run more busses on the full path so there's still ample service for the changes.
How does forcing the 15-minute max path make more destinations available?
You could also just have more lines even if they're long. The length of the lines doesn't change the number of them. It's just a question of how many busses and drivers do you really have and what service interval are you trying to hit.
If you're arguing they should have like a 15 minute hub and spoke model, you might also be forcing some really inefficient routes and once again force people to change busses more when one bus route could have better served the community.