Bought wife QC Headphones, can hear her music 15 feet away with them on. Phone is set to half volume. What’s the issue?

As the title says, bought wife QC headphones today. She put them on her head and I can hear the music 15 feet away. I’m concerned that these will make her go deaf. Her iPhone was set to half volume.

Do the headphones normally leak this much sound? Or is this defective?

Is this just too loud of a volume?