Go to ...
... and copy the file into this folder. Then start the game and load save 15.
If the folder AppData doesn't show, it's hidden and you need to make it visible by clicking on "File" in the top left corner. Choose Options. In the window that opens click on the second tab (must be "View" or sth), scroll down to Hidden Files and Folders and choose to display them.
(I hope the terms are correct, my Windows is in German.)