While the 2015 numbers are startling, marijuana arrests have actually steadily decreased since 2007, when 872,720 people were arrested. 2015 also saw the lowest total number of marijuana arrests since 1996 (http://www.businessinsider.com/fbi-weed-arrest-data-2016-9).
A new report predicts legalizing weed could generate $28 Billion (the equivalent of North Korea’s GDP) in taxes for the United States.
643,121 persons were arrested in 2015 (http://www.drugwarfacts.org/cms/Marijuana#Total). Estimates are $46K per inmate per year for incarceration. That is $29,583, 566,000. That is not a typo. This money can be reallocated in the federal budget.