Is he home by himself during the day?
Generally, even the most difficult yorkie, can be housebroken if someone is home with them during the day. The 24-hour schedule and someone dogging them constantly will soak in.
If you work, is there someone that could keep him during the day and housebreak him?
How did you come to get him at 1.5 years old? He's a doll. That's for sure.