Forza Horizon 2 Backwards Compatibility

The Xbox One introduced backwards compatibility with the 360.

Forza-Horizon 2 for Xbox 360 and the One are completely different games.

I have the 360 version, the smaller map, less glitches (I want them). If I put this disk in the One, what version will I play?

The better, Playground Games version, or the limited, smaller Sumo version.

Backwards compatibility doesn't mean your titles will upgrade to the next gen version (like Call of Duty, Destiny, sports games, etc.). The Xbox One will run the 360 version, if it supports it(not certain if FH2 is back compat as it has its own console version).