Does the module have the ability to refresh sales prices for groups of customers, e.g. every 15 minutes?

>Does the module have the ability to refresh selling prices for groups of customers e.g. every 15 minutes?
>E.g. every 15 minutes to check the purchase price (whether it has changed) and add our margin?

Yes, you can insert this process in CRON so that it happens automatically. Note that this is one margin for all groups.
To set individual margins for groups - you need to add individual margins set for groups. Such markups do not change the prices definitively in the database, but it changes the prices for customers from a given group on the store. For more about changing prices “live”, see the module description on prestashow.pl