Why did the south favor the 15th amendment being passed?

The south favored it because African Men had the right to vote 

I don't think the South necessarily favored the 15th amendment. The 15th amendment gives black people the right to vote. Seeing as the South just came off of a loss in the Civil War which was fought in part because the Confederation was fighting for the rights of the states to own slaves. Southerners didn't like that their former slaves who were thought to be inferior were now raised to the same status as their white owners.