when i write:
import flash.display.*; // importing all the classes of display
import flash.display.MovieClip; // importing only one class
and likewise other classes, so the question is: If i import all the classes from some package the application will work more slowly than if I import only the REALLY needed classes?
is that true or false?
That would be false. Importing more classes from the namespace should not affect the speed of your application as it does not cause any more code to be run.