2015? Stop using Final Cut Pro and playing games on it, and uninstall Flash if you have it installed. The Final Cut Pro one has a good chance of being an obvious thing that you can't stop using, so ...
Those things are using a lot of CPU, and GPU if it's dedicated, so the fans will turn on to reduce risk of your system overheating. From least to most invasive:
1. You could get a cooling pad, even one with its own fan(s), to assist keeping the temperature from getting high enough to speed up the internal fan(s), but one with its own fans could end up just making the whole thing even louder.
2. Take the bottom cover off and clean out any dust that may have accumulated there since you got it, using a can of compressed air.
3. Some people have re-applied the thermal paste inside the system, but if you're not familiar even with that phrase, then don't bother doing it yourself ... Better off asking apple to do it at one of their stores. If you have AppleCare, they might do it for you ... It depends on the person that helps you. At any rate, this option has mixed reports of success, so I'd only consider it as a last resort, and wouldn't bet on it helping in every case.
Have you tried getting a stand to keep the system elevated off the table or desk surface? Some people claim that helps. I keep mine elevated, but I never had a problem like yours (I use a PC for gaming), even before I got the stand, so nothing to compare it to in my case.