Lag time filling in Adobe forms

I've created a fillable form. Every time I use the tab key to move to the next fillable box a little calculator icon appears and it takes a few seconds before I am able to fill in the next box. It looks like Adobe is refreshing itself after teach tab key action. The lag occurs only when a value or text box is populated. This form is a timesheet and there are many fillable boxes and the long lag time makes it unusable.

Please can you help.

Thank you.