Social Security Lock-Box Act of 2015

Amends the Congressional Budget Act of 1974 to provide a point of order against consideration of any: (1) budget resolution that sets forth totals for any fiscal year with respect to the Social Security Trust Funds that are less than the totals of the Social Security Trust Funds for that fiscal year as calculated in accordance with a current services baseline, or (2) spending or tax legislation that would cause any totals to be less than the Funds totals for the covered fiscal year.

Makes the point of order described in (2) above inapplicable to Social Security reform legislation.

Requires any federal budget submitted by the President that recommends totals for any fiscal year with respect to the Funds that are less than the totals of the Funds for that fiscal year to include a detailed proposal for Social Security reform legislation. Makes this Act inapplicable upon the enactment of such legislation. Defines "Social Security reform legislation" as a bill or joint resolution to save Social Security that specifies that it constitutes reform legislation.