InfoPath Dev

I create the infopath form when user fill the form that time it take a time to move next fields. Suppose User fill the First name and user want to fill the last name that time user need to wait for same time to move on Last name.Why it take time its very slow. I select the option for offline mode.

 Is this in the browser or the filler? Does this reproduce in a new view? Is there a lot of logic on the First Name field?

Its Filler. Actually problem is in my drop down field where i bind the data from sahrepoint list in this list data is large.