Sure, because illegals mailed in their Census. You’ll be closer to the true number by checking school enrollment.
The 2015 census is based on estimates from a variety of sources. Recall we had no census to send in that year.
School enrollment is just one indicator, but is skewed due to differential fertility rates.
It DOES indicate future demographics to some degree - but if you used the 1970 school demographics to predict the population of both Texas and California 20 years later, you would have been totally wrong.
So the Anglos of Texas ain’t dead yet. We’ll see as the current enforcement regime goes forward.