Here are the correct question tags for each sentence:

1. I'm a bit fat, **aren't I**?
2. There used to be a stadium here, **didn't there**?
3. Turn off the fan, **won't you**?
4. In big cities, life can become very difficult and unpleasant, **can't it**?
5. The world will soon become overpopulated, **won't it**?
6. The number of English speakers is increasing very quickly, **isn't it**?
7. Jeju Island looks very peaceful, **doesn't it**?
8. I think a megacity is a very large city with a big population, **don't you**?
9. You have never watched any films made in Bollywood, **have you**?
10. Some people commit crime when they have no money and no food, **don't they**?
11. You enjoy living in a peaceful neighbourhood, **don't you**?
12. The factory will bring more jobs to local people, **won't it**?
13. You forgot to bring your textbooks this morning, **didn't you**?
14. Come to my party, **will you**?
15. Don't smoke in this room, **will you**?