I got my 2016 Journey Crossroad about 4 months ago and have had the same exact problem. It will only fill it up to around 14.5 gallons after the low fuel light comes on. One time I got it to fill up a little over 15 gallons after driving a couple miles beyond the point that the "low fuel" light came on, but it was seriously only a few miles. I called the dealer and they told me the reserve was 5-6 gallons and that there could be nothing that would cause something like that.
The fuel gauge never shows that it's completely full after a fill up either.
A friend suggested keeping a gas can in it as well and to drive it until it dies to see how much I can pump in afterwards. I drive a lot for work and it's all interstate, so it's hard for me to plan a good possible location for my car to run out of fuel. Especially since it's so unknown as to how many miles I will make it after the light goes on before it happening, but I should be able to try it out tomorrow. Will report back.
Just so frustrating.
