You haven’t said how you want to limit the fields. If you are looking to do something like only allow 15 characters you can use either the Input Translation field property to just remove the excess cahracters or the Input field Validation property to Give the user a warning message.
Both these methods use the Lotus @functions to build the formula used to verify the entry.
You can use the Exit Field with Lotuscript also but it only validates if you progress to another field. If you enter then save the document it isn’t triggered.