Not sure where you read that, but Apple went through this exact problem several years ago . Kids spending literally hundreds of dollars because once mom entered the store password, they didn't need it again for 30 minutes.
After that , they NICELY refunded all those silly transactions and then made it require a password FOR EVERY PURCHASE.
If 7.1 gives a 15 minute window, that's brand new and backwards from their previous direction.
I'm on 7.0.6 now, requires a password for ALL purchases, even 10 seconds apart