State Partnership Program Enhancement Act of 2015

Amends the National Defense Authorization Act for Fiscal Year 2014 to revise and extend indefinitely the authority of the Department of Defense (DOD) to establish exchange programs for members of the National Guard under the National Guard State Partnership Program (SPP). (Currently, the authority is scheduled to terminate on September 30, 2016.)

Authorizes DOD, with the concurrence of the Department of State, to establish such programs for exchanges of members of the National Guard of a state or territory and the military forces or security forces or other government organizations of a foreign country to support the national interests and security cooperation goals and objectives of the United States as defined by the current and evolving national global strategic policies of the United States. (Currently, the primary function of the SPP is disaster and emergency response.)

Directs DOD, with the concurrence of the State Department, to establish procedures for SPP planning, programming, budgeting, accounting, and performance metrics.

Requires the National Guard Bureau to: (1) maintain a list of core competencies of the National Guard to support SPP activities, and (2) designate a director for each state and territory.

Requires DOD to coordinate SPP regulations with combatant commanders to ensure that program activities meet theater security cooperation objectives. Requires the State Department to coordinate such regulations with relevant chiefs of mission to meet diplomatic objectives.

Establishes the National Guard State Partnership Program Fund in the Treasury, into which appropriated amounts shall be credited and transferred for program activity uses, including payment of costs for personnel, training, operations, and equipment.