I recently purchased the Sena leather wallet case for both the iPhone 6s and 6s plus. I think it would dramatically improve the functionality of the wallet for the 6s plus by: 1. taking advantage of the longer case by adding one more car slot. 2. extending the length of the wallet as it is currently configured it is just short of putting cash in without the need to fold it, this reduces the amount of cash you can carry or conversely unnecessarily adds to the thickness.
Sincerely 
Lew Fanwick