The engine is very clearly an evolution of the DS2 engine. There are literally dozens of indications of that you find just by a cursory look.
I have a random question, from your current experience with the game, do you think DS3 surpasses the graphical quality of DS2's initial reveal (pre-Downgrade)?
DS3, like Bloodborne, definitely has more complex geometry when it comes to environments, but I have to admit that the original DS2 reveal still looks absolutely stellar, even compared to DS3.