like someone said above, do not bother with the promethazine. It just makes you more sedated and I find it "clouds" my opiate high/euphoria. 15 mg is a perfect starter dose, you should be feeling pretty good.
I take opiates once a week and have tried many methods of potentiation. The best is grapefruit juice, it's the only one that actually intensifies the hydrocodone instead of just adding another element (usually sedation) to the high.
Thanks for the advice, any other tips to improve the high?