Is $8,500 to paint living areas, hallways, trim, and doors a fair price?

The contractor is using two different sheens and paints (Promar 200 and Emerald Matte) for the base coat on walls/ceilings before applying the final Emerald Matte coat. Sherwin Williams advised against mixing different brands and sheens, even if the final coat is the same. I am concerned about potential streaking and the quality of the base coat impacting the final finish. I am also questioning the amount of paint purchased (15 gallons of Emerald) versus the number of coats being applied, wondering if I am overpaying if a cheaper paint is used for the first coat. The house has 19 ft ceilings in the living areas. I am comparing this quote to a previous one from 3 years ago ($9800 for the whole house, but not using Emerald paint) and feel hesitant.