There are a lot of fire expert consultants available, so you should get another opinion. Google “building regulation consulting” or “fire regulation consulting” for your area.
You do not have to accept the proposal of your current consultant – they should be taking into account the age of the building (ie, the building code when it was originally built) and its architecture, as well as the costs of the work.
You could go back to the consultant and ask for another design without sprinklers, or if they must be added, then ask for the reasoning, and then talk to another consultant and check the reasoning is valid, or must be applied.
The building code on fire regulations is complex, and there is usually a solution that better suits your needs. It’s like when you consult a lawyer, doctor or architect – if you don’t like their advice, get another opinion. If several all agree, then you are probably stuck with making the best of it.