The new train line is going to be 160km shorter while also allowing higher speeds. Trains between Hamburg and Copenhagen are projected to take less than 2:30h, down from 4:40h today.
Jokes aside, there are sometimes rail projects where millions are spent to save 2 minutes. Or even just tens of seconds. Over the lifetime of the infrastructure it is still worth it, especially when combining multiple projects.
2 hours savings is huge. You won't find many infra projects with those kind of time savings.