Well, as everyone has said, the speed of the ball of the pitch is primarily dependant on the pitch. If the pitch is green, and slightly moist, the ball will skid onward, and won't lose much speed at all, probably only around 10 km/h.
Whereas, on a 'sticky wicket', one that is dry and has lots of cracks, might slow a ball up by around 30 km/h.
This is all negating the air resistence, which would slow the ball by around 5-10km/h. As such, a ball released at 150km'h could slow to anywhere between 130 km/h and 110 kmh, depending upon the wicket. Both of these are still awfully fast for a batsman to face, and still rather difficult.
And also, how the ball was released would have some minimal effect upon the spped of the ball, because if the seam position is upright and remains so, the ball will move marginally faster than one released with a scrambled seam.
Hope this helps.