Greetings Chetiar, I had to convert all your measurements to meters before I understood how large your room is! I used to have D38's, and my room is slightly bigger than yours (5m x 8m x 2.5m). It worked beautifully in this room, but you need to have some flexibility in placement. My final configuration had them 1.5m (that's 4.5 ft) away from the front wall, and 1m (3 ft) away from each side wall, with 3m (9ft) between them. I sat 3m away, so got a nice equilateral triangle.
The D38's will be a nice upgrade from your D15's. Go for it, and good luck.
The D38's will be a nice upgrade from your D15's. Go for it, and good luck.