Mafia 3 has heavy graphics filters that impart ugly sepia tones, blur textures, and mute colors and reflections. What helped for me a lot was installing a graphics mod that alleviates these problems, but it also actually made it run noticeably better.
It's a little tricky to install, but this guide is good and worked for me.
View: https://www.youtube.com/watch?v=FqnRybaYPqM
That said, later updates for Mafia 3, while solving some of the known graphics bugs, actually added more than it fixed. The games graphics bugs are more of a problem than the performance, especially later build versions on W10. There are places in the game where you'll see really nasty black triangles emanating from NPCs which look like bad artifacts. Before the more recent updates it was limited to a few places that could be avoided by going into the small thrift stores during the day. Now they can happen anywhere, including outdoors.
It's really a shame because other than these problems, it was pretty good game.