15 a month for unlimited gameplay, you can play it as often as can/feel like. That's cheap. One night out to dinner costs that or more. A non-sub game is going to run you 30+, that wont be near as time sinky. Best part about WoW is that you can suck your friends into it and make it just as social as going out to eat. Obviously you should do things outside as well, but honestly, WoW, for being able to play it any time and as often as you could ever want, is a good deal.
The real regret lies in the areas of paying for it when you don't play, or having no self control and becoming a basement dweller over it.
I bet that if you take that same amount of cash, go back in time, never purchase WoW, you'd have blown it in 1-6 months. Let alone over a year or more.
If you had fun, it served its purpose.