What aircon do you need for 15 square meter room?

That depends... Do you have Windows in this room? How large are they? How long do they spend in the sun? What is your insulation like? Do you ahve any doors? Are there any trees that might shade your roof? Calculating a proper AC unit for a room or house isn't as easy as it looks as you must account for heat gain from various sources. Consider consulting a reputable AC dealer or service company in your area.