I've just spent an age trying to work out why 14A Nickname of the US state of Detroit (sic) which I had assumed to mean Michigan and therefore the answer should be "MITTEN" and 15D Deciduous tree also called gean "WILD CHERRY" wouldn't fit together.
I've now realised that the answer to 14A is MOTOWN and therefore the clue did refer to the city Detroit. Since when has Detroit been a state?