A possible solution:
Verizon rep had me go to Cellular in settings, then to Cellular Data Options.
Then to Roaming.
In Roaming turn on Voice Roaming, Data Roaming, and finally turn on International CDMA.
Then TURN OFF the phone and restart.
Voila, the Tested speeds on Data on the iPhone 7 magically increase.
Didn't help on my iPhone 6 Plus but did work on an iPhone 7.
Maybe the promised improvement in 4G LTE advanced is really there.
I'm waiting for my new iPhone 7 Plus to see for sure.
But this was an outstanding tip - learned it on a 611 call !!