FFXV was sold for 20 EU 2 years after release. That sums it up, loads of unsold copies in retailers. Overshipped game.
Sums what up? That those unsold overshipped copies of FFXV still sold more than FFXIII?
OT: Since PS1, it seems like every big FF games has about 2-3 year gap while FFXV to FFVIIr has a 4 year gap. So dont expect a new big FF game until at least 2022. It wont mean FF16 will be next but more likely another FFVII remake part 2.
I dont think Square is scared to release FF16 but more likely they just want to take their time or have other projects in mind like Kingdom Hearts or Project Aitha etc.
As well, Square hasn't been "traditional" in a sense of releasing games numerically one after another as their big FF game since after FFX. We can no longer assume that Square should be working on FF16 (ie. Square didnt release a FFXV last gen but rather focused on FFXIII-2 and FFXIII Lightning returns)