They make a 15" snare in that size too. Never thought about going bigger in diameter over depth, but they make a good argument on their website:
"In my opinion, a 5.5x15 snare should be a staple in every drummer's arsenal. Huge sound, but surprisingly sensitive. They can go lower than any 14, but also tune up to higher pitches and really sing. I think a lot of people try to go with deeper 14's for a deep sound, but they really need to try a larger diameter. We have found the 5.5" depth to be the perfect balance between huge tone, and manageable responsiveness."