It could also explode if, like most real meteors, it's made of more than just a single material and gets hot enough so something inside (whatever it is) gets vaporized and the outer hull can't keep the pressure any more. Say, frozen water inside, or anything. Even "inert" materials like iron and stone will become liquid and eventually boil, if you only make them hot enough.
About the size of the explosion, just consider the formula for kinetic energy. 10k tons are a huge number for m and 15km/s is also a terribly huge number for v2
Very likely, as you can tell from the fact that no civilization we know of has been wiped off the planet during the last 6,000 years. Besides, 2 seconds are an eternity at such a speed, it's not like two seconds before impact are anywhere "near the ground".
Also, it went at 15 km/s and exploded 30km above ground. If it exploded 2 seconds later it would have hit the ground. How likely was that?