What is the breakdown of the per line costs? DPP agreements? Contract? Insurance?
I'm most definitely NOT a VZW employee. If a post answered your question, please mark it as the answer.
Do you use 15GB of data each month? Are the phones currently under contract, or on a device payment plan? Without details of your current plan (name of the plan), access fees, other costs that may or may not be changeable, we can't tell you how to reduce your costs.
If you were to change plans to get a "better deal", you would need to look at current plans - which are 2, 4, 8 GB, then unlimited. Base cost for those data plans are $35, $50, $70, and $110. Add 3 lines at a minimum of $20 each, potentially $40 or more each if they are still in contract or have a device payment attached. Insurance? More details will help us to help you figure things out more accurately.