I do get the value of limiting further in-app purchases without reentering your password.

Among the new features of iOS 7.1 is the addition of a warning message for users concerning the 15-minute in-app purchase window. This quarter-hour window allows you to buy IAPs on an iOS device without further authorization for 15 minutes following the correct entry of a password.

But why 15 minutes?

The feature (which can be turned off in the “Settings” menu) is likely related to Apple’s settlement with the FTC, which saw the company refund $32.5 million to customers on the back of a lawsuit over IAPs. At the time Apple said that it would not only issue refunds to those affected, but also modify its in-app billing system to make the process clearer for users. These changes came with a March 31 deadline from the FTC.

Ah, makes sense. Sort of like saying, “How much trouble can someone get into in 15 minutes?”