I use the 15's because I have sensitive ears and figured 9 wasn't going to be enough. I can hear fine with them, although if you walk away and someone is talking to you it takes less distance before you can't hear them. Bass wise, I do notice I can't tell how loud I am (first time I've ever been told to turn up!!!) so I have to rely on the guitar/drummer to tell me if my volume is good if I forget to check it before putting them in. I can actually *hear* myself with them in......instead of my ears cringing in horror and shutting down.
The auditory specialist suggested I get the 15's when I told her I played in a rock band in tight areas. She said if I were in an orchestra she'd suggest the 9s.......a thrash band she might suggest the next ones after the 15's

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