If you open an app on the iPhone 6 and close it after using, then the app is not completely closed, but almost frozen. This will allow you to open the app on your iPhone 6 again quickly and without long waiting times. But if you want to close or terminate an app properly, then you must do the following steps on your iPhone 6:
To close an app on the iPhone 6 tap twice quickly on the Home button. The currently displayed screen will shrink and you will now see all apps and system applications in a small Task Manager, which are "frozen" in the background. To close an app completely swipe it up and out of the display. Thats it!
The app is now completely closed and away from the RAM (memory) of your iPhone 6. If you now open the app as usual, this will need a bit longer to open than would previously have been the case. However, this should not fall in the weight because of the speed of the iphone 6.