Yes, there is a difference between the phones' thicknesses, but not as significant as the increase between the cases. And there is definitely more side surface area for grip on the new one... this Sheath almost feels Otterbox-like compared to the old skinny guy on the 12PM.That’s interesting to see the difference in the 12 vs 15PM Sheath, but I think it may be largely due to the difference in the phones dimensions. I compared via Apple website & 12 is 0.29 inch depth while 15 PM is 0.32 inch depth.
This is my first year with Caudabe, but I have read others saying the same as you, that this years sheath & synthesis are more similar than previous years.