If the electrical system is properly designed, circuits are generally protected by circuit breakers or fuses at their source. The circuit breakers or fuses are matched to the wire size used for that circuit; if the load on the circuit is more than the wires can handle, the circuit breaker or fuse opens the circuit.
Different electrical codes are adopted in different places to standardize the design of these systems. In the US, the National Electrical Code would allow a circuit fed by a 15 amp breaker or fuse to use 2.5 mm^2 / 14 AWG wire; that wire can handle that load. If the standards are similar in your location, your 2.5mm wire is fine for a 15A circuit.
Your air conditioner draws 1550 watts at its rated 220 volts, which translates to about 7 amps. At a lower voltage, it may draw more current - at 180V, if the power / VA draw is similar, it will draw around 8.6 amps - still well within the circuit's 15 amp max.
Of course if there are other receptacles on the circuit, there may be other loads that could add up and overload the circuit and trip the breaker or blow the fuse - but the air conditioner alone leaves quite a bit of room for other loads on a 15A circuit.
At 240V, if the air conditioner tolerates the higher voltage, it will draw less current. As long as the insulation, receptacles, breakers, and other components tolerate this slightly higher voltage - which they almost surely do - there won't be a problem with the electrical system.
Voltage stabilizers are rated for the load they can handle. Since the air conditioner draws only 1550VA and the stablizer is rated for 4000VA, the air conditioner is well within the capacity of the voltage stabilizer.