> As for CO2, the plane flying slower is more fuel-efficient. Isn't this lower CO2 emissions?

It is not only about fuel. Right? Article is talking about punctuality. People will use competitors if an airline is not on-time. So with padding they create a safety gap to make sure they arrive on-time.

I believe 15mins safety gap is fair as it is extremely difficult and expensive to always operate on-time without a major airport redesign and technological advancement in how the system works. It gives passengers a reliable arrival time to plan whatever they have next.