16mm is big for a hand drill .. you dont state the type, so hard to know the specs, 1000 rpm is too fast too If you dont have enough weight to force the bit down, your progress will be minimal.
All these points have been mentioned, as has this,.. drill a pilot hole first but
as Nasher says..in two stages, I'd prefer 8, then 12 , then your final, by that time witha 16mm, you'll really feel the torque on your wrists believe me
plus you'll probably waste all three drills in the process, cos if its hard stuff they will get hot and not cope, so use water to help with that.. but its the only way for an 800 watt job if is a strong concrete mix ..
If you hit reinforcing inside it, you'll be humped with a masonary bit unless you want to buzz through several
best plug the hole and try another spot, or if that fails, time to get a jack hammer out