DEF - Usage

I read a thread on a travel trailer forum that was discussing DEF. The people were saying they are getting about 1500 miles for their DEF tanks, about 2.5 gallons. That seemed to be the norm they were reporting for their 2500 and 3500 trucks.

I just put in my third box of DEF in my 2500 and I have about 12,000 miles. So I figure that is about 5,000 miles for a 2.5 gallon box. I don't put any more than one box in at a time and only put it in when the gauge shows it is almost empty.

I just read a thread on this site, from 2017, where someone said you should get about 5,000 miles on 2.5 gallons of DEF. That same thread said to turn off or change the amount of DEF used. Is that on older system of DEF that can be turned off or amount adjusted?