It has to do with the migration files and the contents not being of the .15

0.001 2017-05-02 10:50:17; Factorio 0.15.6 (build 29362, win64, steam)
0.001 Operating system: Windows 10 (version 1607)
0.001 Program arguments: "A:\Program Files (x86)\Steam\steamapps\common\Factorio\bin\x64\Factorio.exe"
0.001 Read data path: A:/Program Files (x86)/Steam/steamapps/common ...