Industrial Hemp Farming Act of 2015 Amends the-Controlled-Substances-Act-to-exclude-industrial-hemp from the definition of "marihuana." Defines "industrial hemp" to mean the plant Cannabis sativa L. and any part of such plant, whether growing or not, with a delta-nine tetrahydrocannabinol concentration of not more than 0.3 percent on a dry weight basis. Deems Cannabis sativa L. to meet that concentration limit if a person grows or processes it for purposes of making industrial hemp in accordance with state law.