The “15-minute” city is a term used to describe a type of neighbourhood (or preferably whole city) where, for everyone, all their day-to-day needs can be met with stores that are at most a 15 minute walk or bike ride away.
Transit-oriented development refers to planning the land around transit stations (trains stations, tram stations, etc) to be designed as much as possible with destinations in mind. That means housing, offices and shops, instead of large parking lots for commuters.
The two concepts refer to different things, but they are not incompatible with each other. In fact, they complement each other.
I would say neither is better than the other, and they are best used together.