CfZrx, you don't need to potentiate your 15 mg daily methadone. Just explain to your doctor about the dosage and see how that goes.
The thing about methadone is that it's not meant to make you feel high but to fulfill your need so that you don't go back to your previous drug of choice.
People experience some comfortable/good feelings with methadone in greater dosages. But that's counterproductive as you are using it to avoid being high or using whatever you used before. It's a tool so you can have a 'normal' life. It takes few days to adapt, maybe a week. How long are you doing this?
Maybe 15 mg is rather low to start with. Discuss this with your doctor. Methadone is pretty strong and nothing really makes it so much more potent. It's already strong as it is and long lasting too.
In so many years after stabilizing I remember that once he had to increase it by 10 mg by evaluating its cost benefit issues and it solved all my problems for few weeks but some time later I just adapted to the new dose, making it more distant from getting down to lower doses.
It just makes things look normal. Don't expect for more in a long term treatment. You'll be okay and that should be enough. At some point you won't even crave for your D.O.C.
I've been on methadone for many years and it was extremely difficult to go down. I started with bigger dosages bc I was coming off a very strong opiate at a very high dose. I stabilized at 70 mg daily. But as I mentioned -- going down to your dose was a very difficult thing, not to mention coming off of it completely.
You got this. Send me a PM in case you need to. I've been through this before. Heads up!!