I think it's great, but honestly, placing it at 15€ would have made only a little difference to the consumer, who is already getting a lot for the value, and helped the railway operators a good deal. As a compromise the age of kids who can travel together with their parents for free could have been raised from 6 to 8 years.
Now I think when the times comes (3 month from now) for the program to run out, we might see discussions about continuing it at a price that makes it a more sustainable, permanent offer. But that's my opinion speaking (I wouldn't even mind if it was mandatory like back when I was attending university, as long as it is affordable for people with low to lowest incomes).