Do you both have the same plan? If you both are on the base plan then run the tests simultaneously and compare. Do you both have the same phones? Not really an expert on phone or all that tech savvy but from what I have read the difference in phone antennas could make a difference.
I can run a speed test, actually today even, and get <1Mbps and then turn on and off airplane mode so it will grab a different band or tower and will get upwards of 20Mbps average.
The base is deprioritized data so you are at the mercy of congestion on the towers in your area. The next time you visit you could try and contact customer service and have his line re-provisioned if your speeds are greater than his, it may help but be prepared to spend some time with CS.
Another thing to go into settings and find reset options and reset mobile network(NOT factory reset), if the network reset includes wi-fi and Bluetooth(Samsung is separate, Motorola is all three) you will need to change the name of the hotspot he had back to what it was including password or his device won't connect, any Bluetooth device that were paired will be erased and need to be paired again.
