I agree with seedy that they should have at least offered you something for giving the money back to them. like a really decent deposit bonus, or at the very least 100 free spins on £1 or £2 stake.
If they dont offer anything, I would put the 1500 on the next horse you see at Evens, if it wins pay the money back and still have 1500 for yourself, if it loses say sayonara to the casino.
or spend the 1500 on a holiday and send the casino a selfie of you in the sun saying cheers with a beer in hand