I am a writer. I love writing fantasy books. I've already written two fantasy novels, but now I wanna try a different subject that involves real life matters. Is it a good decision? Cause I write fantasy better than real life issues.

Sometimes you just gotta go with your strengths. If you have sufficient knowledge to tackle a real-life subject then go for it.

I'm facing a similar problem. My last book was an urban fantasy but the real-world subjects I would like to write about require more knowledge than I can easily gather. I'll compromise by moving it off planet. (Keep an eye out for about the same time Hilary Clinton gets the keys to the White House.)

But whichever way you go it's a phenomenal effort to have completed two novels by the age of 16. Congratulations. You should be pleased.

Why would you change the genre of writing? If you are doing perfect in writing fantasy novels, why wouldn't you continue to do it? If you are just bored writing in the same genre, you may add some other genre to it, like for example comedy or thriller, but still it can be your main prospect. Like for example here at http://www.academia.edu/3535067/More_than_Monsters_Dark_Fantasy_the_Mystery-Thriller_and_Horror_s_Heterogeneous_History , it is the best example of combination of novel and thriller, which is perfect and very interesting.