My first audio room was small like yours--13x15 feet. Here is what worked great in that room:
Speakers were pulled off the front wall about 6 feet and then 2 feet from the side walls and toed in to the listening chair which was just off of the rear wall forming an equilateral triangle.
Treat first reflection points on the side walls and then behind the listening chair with rockwool panels. Making your own is way cheaper and just as good or better. If you want premade panels, check out Audiomute, priced better than GIK and some of the other routine recommendations.
I tried multiple speakers in that set up and the all sounded great with an stereo image that made that small room sound HUGE.