Diesel pumps via 'auto' nozzles should flow at same rate gas nozzles do.
If they are flowing slow there is a problem with the delivery system:
Filters, pump, nozzle
Use a different station if that station shrugs off the problem.
I can fill my 35 gallon diesel tank just as fast as I could fill a 35 gallon tank of gasoline.........provided the delivery system is functioning right.
Now the ones at truck stops......whoa boy! They will flat out fill that tank in about 40 seconds.
That's why there is always fuel on the handle, the pump platform, the ground........