Start at like .5mg or even 1mg - the increases can be absolutely brutal. I was doing just fine on 1.5mg and went to 2 and had the worst GI sides , Reta lasts like a week too so its just gonna be a rough week.
But, it has to be said, Reta wont magically make you under 10%, its a tool, like actually gets less effective at body fat levels like yours, diet, cardio, carb timing etc will be the heavy lifter, the only thing reta will really add for you is appetite suppresion, your likely already getting majority of the insulin based benefits just from being lean.