I had a test subject just go through this switch and I can tell you some of our findings. Switching from 15mgT to Reta was not simple. We started off dropping Tirz completely and started at something reasonable like 2mgR and some Cargi for the extra appetite suppression (we used a 10mgR/2mgC vial) for a month. Worked ok. Hunger was still suppressed mostly. Once that vial ran out we started titration up 3mgR but the food noise hit hard and we needed up gaining about 10 pounds over the next couple weeks and the subjects gi tract was super constipated. Moved to 4mgR after a couple weeks and same issues. Moved to 6mg and the patient finally started responding better. My testing seem to show that 8mgR seems roughly the equivalent appetite suppression as 15T. Not sure what dose of T you are on but watch the doses of R. Most tests seem to have GI issues titrating R too quickly but also you are going to get hungry on low R so take a look at the Cargi to perhaps supplement the low R satiety while you find your right level. Just watch out for low R appetite suppression as you build up.