Zoom and Pan in Real time - too slow

When open any drawings with very more blocks and layers I have observed the following problem :- when try to make a zoom or pan operation in real time, the drawings is regenerated after over 5 seconds.The result is that after move the mouse cursor, the drawings is moved just after over 5 seconds, or in domain like road design, when I have more blocks and more layers this problems is very vexatious.Liviu