Not sure why... but it seems that it's okay now on this test release, 25-30 FPS... It seems that some option causes it to go slower, but I don't know which is it. During gameplay, it's 15 FPS.
1.9.2 gave same results, though sound was more choppy. So it seems that optimized release managed to speed up sound, but not the game. I can't be still 100% sure.