you not pass the twitter limit yet. when u got 2k followers then you will get 10% add more following rule
Thats really good considering the average non-celebrity gets only 300 followers so you must be doing something right assuming that's 1500 quality followers.
That's great. But it would also be better if most of your followers are from your targeted area or country to increase your conversion.
No.. no it's not that. It's just in regards to how many people you can follow until you get to 1800ish. This is to combat spam followers and I'm not sure about the specifics, i have heard you can follow an added 10% after reaching a certain number of followers.
I too have 1500+ follower in twitter. Its because of few reason, you might be not active, you're making spam tweet, or you're tweeting 50+ tweet a day.