iPhone 6s Plus display suddenly dim
So I've had my (gorgeous, amazing, huge) iPhone 6s Plus for about a week now, and it's a fantastic upgrade from my battered old 5s. Yay! However, I noticed this morning that my display is suddenly oddly dim - nothing drastic, but noticeably dimmer than it has been since I bought it.
I just put it side-by-side with my wife's 5s (with both at max brightness, auto-brightness disabled), and hers is SIGNIFICANTLY brighter, and the issue persists even after a reboot.
Anyone else seeing this? Is there a hidden brightness setting that I might've triggered somehow?
iPhone 6s Plus, iOS 9.0.2, 128gb AT&T edition