Mutual Bank Capital Opportunity Act of 2015

Amends the Federal Deposit Insurance Act to authorize a mutual depository to issue mutual capital certificates that qualify as common equity Tier 1 capital for purposes of capital requirements mandated by federal law or regulation.

Defines "mutual capital certificate" as a financial instrument issued by a mutual depository that entitles the holder to a payment of fixed, variable, or participating dividends (if its board of directors so declares) but no voting or member rights, nor is it redeemable until five years after issuance.

Defines "mutual depository" as an insured depository institution operating in a non-stock form, including a federal non-stock depository and any form of non-stock depository provided for under state law, whose deposits are insured by an instrumentality of the federal government.