How often does the Prestashop marketplace module integrate orders?

At the frequency you want. By default, orders are integrated every 15 minutes if you are logged into your Prestashop back office. You can also schedule a cron job and integrate the commands at the desired frequency.

Sellermania continuously polls marketplaces, regardless of what you choose for your Prestashop. You are then free to define how often you want to integrate marketplaces on your Prestashop.