I own a rental property and have been trying to sell it. The deal collapsed and I received $12,500 of the buyer's $15,000 deposit. Is the income taxable?

Yes, that is taxable income. It would be Miscellaneous income (not capital gain) since it was not for a sale, but rather for breach of contract.

To clarify, the escrow deposit was 15,000 when the deal fell through, so normally you would get the entire 15,000. 

You must have signed some sort of listing agreement that allowed the Listing real estate agent to keep 2,500?  So, you only received 12,500?

And then the real estate agent took another 2,343.22? Or was this the Selling agent? (The agent that represented the Buyer that backed out)

If you ended up with 10,156.78, yes, that is taxable income. 

Did these two agents also sell the property? Usually commission is only paid once the property actually closes sale, so you might want to check to determine if the commissions are selling fees and reported when you report the sale, or simply subtracted from the escrow that was retained. 

If unsure, ask the Closing Agent at the Title Company (or bank) that you used.