When i add a new object using Name mapping then it took too much time to add a object

Depends a lot on what is being mapped.

My gut instinct tells me that you have the option to "Use extended find whenever possible" set to true.  And that a parent object of the object you are trying to map may have that option turned on.  What "extended find" does is execute a search down the tree for the object... and this takes time.  I usually recommend to turn that option in Tools | Options | Engines | NameMapping off and only turn on "extended find" when necessary.