96150 is a health and behavior assessment. The 90804 is a psychotherapy code. Are you billing for a behavioral health provider?
My behavioral health providers bill the 96116 for the bariatric mental health assessment (assessment of thinking, judgement, etc.).
If you are not billing for a behavioral health provider, I suggest using an established patient office visit code based on time counseling, rather than 90804. 90804 requires a mental health diagnosis code in order to be reimbursed by most insurance carriers. Preparing a patient for bariatric surgery doesn't seem to be a mental problem.