When determining the appropriate air conditioner size for a room, factors such as room size, insulation, ceiling height, and heat-generating appliances need to be considered. The general guideline for selecting the cooling capacity is to have approximately 20 BTUs (British Thermal Units) per square foot or 215 BTUs per square meter of the room.
For a 12-15 square meter room, which is roughly 129-161 square feet, a 0.5 HP (Horsepower) air conditioner may not be sufficient. Typically, a 0.5 HP air conditioner has a cooling capacity of around 5,000 BTUs per hour, which might be too low for effective cooling in a room of that size.
A more suitable option would be to choose an air conditioner with a higher cooling capacity, such as a 1 HP unit. A 1 HP air conditioner usually provides around 9,000-12,000 BTUs per hour, which should be more appropriate for cooling a room of that size.
Keep in mind that these are general guidelines, and other factors specific to your room may also influence the cooling requirements. It's always a good idea to consult with a professional or refer to the manufacturer's recommendations to ensure you select an air conditioner that is properly sized for your specific needs.