It is true that there will be a new SAT in March of 2016. You can only take the new SAT after this. Do not worry, there will only be small changes with the grading procedures that make it different (for example no penalties for guessing a wrong answer!)
You won’t be able to take the old SAT after the new one is out, but the new one is a lot easier and, in my opinion, a more accurate measure of your skills.