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.)

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 Department of State 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.