With your budget Europe will not be a very good choice for you (unless you want follow those 4 days 3 nights package tour, but that is not worth while travelling to Europe you should stay there for at least 10 to 12 days then you can see more things) that is because Euro against HK$ is high now is around HK$10+ to 1Euro.
I will suggest you can go to 麗江 or 西藏. I have been to Li Jiang and that is a wonderful place you can also go to 瀘沽湖 和香哥里拉.
You can take a look at this link for more information.
But I will suggest not to follow a tour from HK you should there yourselves and join a local tour there.
http://www.ljtour.com/
I have not been to 西藏. But many of my friends been there before and say that is a very beautiful place.
Pls take a look at these two link
http://www.tibettour.com.cn/cms/
http://www.tibettour.org/c_chinatibettoursite/moban/index.asp.
I think with the amount of HK$15,000 should be more then enough for you to any one of these two places.
BTW I don't suggest you travl with a stranger. You should ask around among your schoolmates or classmates
Hope that you can help u
