Weaning off QUEtiapine after 15 years

I've been on QUEtiapine XR as well as Venlafaxine for about 15 years. I'm bipolar with severe bipolar depression. My current dosage is 400 mg of QUEtiapine and 300 mg of Venlafaxine. I have a new psychiatrist and since I'm no longer stable he is weaning me off both so he can change my medication in a month. How hard is this going to be considering how long I've been on it? He has prescribed Ativan to help me through the rough days but he doesn't want me to take it every day. I have to admit I'm worried about coming off both if these meds.