You are not taking into account the laws of motion that govern all objects in movement and what happens to them when subjected to other forces.
You are making the common mistake of considering the complete mass of the top, but failing to consider the complete mass of the bottom. This will
make your calculations inaccurate, as it will ignore the resistance the mass of the bottom that would have to be overcome.
If you consider all the mass of the bottom, and account for equal opposite reactions and momentum conservation, it becomes obvious 15 floors can not
cause 95 floors to be crushed completely before the 15 floors are all crushed themselves, thus making the complete collapse impossible.
We know floors were crushed during the collapse, the top floors could not stay intact while crushing the floors bellow them. Even IF two bottom
floors were crushed for ONE top floor, there still would not be enough falling floors to completely crush the bottom floors.
Each level had to have the ability to hold the weigh above it, plus the safety factor. The core columns gradually tapered from bottom to top...
Here is the core columns data... wtcmodel.wikidot.com...
How did the core telescope itself against the increasing mass, path of most resistance?