Is it normal for three rooms to be wired to one 15A circuit breaker?

that might even be illegal it's certainly against code, as none of the circuits is fully protected to its maximum(theoretically only 5 amps each) aside from that if the air conditioner is one with an air hose that goes out of a window or door they are hugely inefficient and expensive to run they use cooled air in the room to cool the heat exchanger so it is constantly pumping expensive cooled air out of the window, because they pull thousands of cubic feet of air through the room they also make rooms dustier and dirtier, a portable split unit is far better and can actually save money