I have always had a Motorola Droid phone and this month I decided to get a samsung galaxy s5 . Well long story short my data usage has more than doubled having the s5 and I have no changed anything different than with my other phones in the past. I usually don't even use 2gb a month my billing cycle is about to end and I have already used 80 percent of the 10 gb I have.on my plan.
sounds like the device might be trying to back your phone's content up to the VZW cloud? I think I have it disabled on my phone. If you want to use it, make sure it is set to Sync via WiFi only to avoid data usage.
You should be able to determine what is consuming Cellular data bandwidth.
Go into Settings | Mobile Data or maybe it's Mobile Network. You can even press the menu button and enable the display the programs using your WiFi.