The USPS delivery status "Origin Post is Preparing Shipment" means the package is being fully prepared before it is shipped out. This status is common when a package is being sent from one country to another.
Foreign shipping companies consolidate a number of packages into one shipping container before it is sent to another country. This is the most common reason for the "Origin Post is Preparing Shipment" status. This status is also the last status before the package enters the mail stream of the destination country. The amount of time a package stays on this status largely depends on how many packages are coming from the originating country to the destination country.