I recall 40% louder. We'll see...
I just checked and I did remember correctly.
Apples are saying the iPhone 7 speakers will be TWICE as loud 2x, AND have a wider dynamic range, so not only twice the volume but better quality at the same time.
Check this video here, and move forward to the 1:19:25 in this youtube video link:
Looking forward to hearing real people's opinions when the play their iPhone 6s next to the new 7 and get their reaction.