Drunk Driving Repeat Offender Prevention Act of 2015

Drunk Driving Repeat Offender Prevention Act of 2015 Directs the Department of Transportation to withhold specified graduated percentages of a state's apportionment of certain federal-aid highway funds for FY2018-FY2020 if the state has not enacted and is not enforcing a law requiring the installation of an ignition interlock device for a minimum of 180 days on each motor vehicle operated by an individual convicted of driving while intoxicated or driving under the influence. Defines "driving while intoxicated" and "driving under the influence" as driving or being in actual physical control of a motor vehicle while having a blood alcohol concentration of 0.08% or greater. Requires an ignition interlock device to: require a driver to provide a breath sample before the motor vehicle starts, and prevent a motor vehicle from starting if the alcohol concentration of the driver is above the legal limit. Authorizes reduction of the 180-day period to 90 days if: the driver's license is suspended for a minimum of 180 days as a result of the conviction, and the period for installation of an ignition interlock device begins after the last day of the suspension.