What is the applicable Building Code - or - if no Building Code is adopted, what applicable NFPA standard are you designing the building to? This will govern the requirement for fire protection.
NFPA 415, Standard on Airport Terminal Buildings, states that a terminal building with an area greater than 12,000 square feet requires automatic sprinkler protection. See section 4.5.1.1.
Lowering the sprinklers won't work. This is a violation of the standard governing the installation of sprinklers (NFPA 13) because the link must be heated to operate - this heating occurs when the ceiling gas layer reaches a temperature that is equal or greater than the fusible link or frangible bulb after the thermal lag time has been overcome.
Concerning the ability of the ceiling sprinkler to operate, this is a function of sprinkler's detection link sensitivity to a given fire producing an estimated heat release and burning rate. In your case, it may be appropriate to mathematically model the conditions. Software such as DETACT is available to determine if the sprinklers will work. I caution you to not go down the road of finding and downloading the software and populating it with ill conceived values for the variables. Other variables like building geometry and ventilation will influence the outcome. Seek professional assistance in this case unless you are qualified to perform such an analysis.
If a performance design is chosen which will be used an equivalency to a requirement in a standard or code, documentation of the design fire conditions is crucial. An example is a design fire based on wood and cloth furniture. After the building is opened, all of the furnishings are replaced with furniture formulated with plastics. This produces a fire with a higher heat release rate and faster burning rate.
