When you download Farming simulator 2015 mods you shoud do these steps:
1. If this file is .ZIP these will don’t need to be extracted you shoud move this file to Documents\My Games\FarmingSimulator2015\Mods.
2. If this file is .RAR you need to extract all the files to your data folder.
3.If this file is .EXE just double click on it and when it runs.
Only ZIP files will work in the mods folder. RAR files will not work