Commencing October 1, 2005, there is provided an increase in benefits to certain persons identified in this section who are currently receiving benefits whose effective date of retirement was prior to October 1, 2004, for purposes of receiving benefits from the Employees’ Retirement System, and to certain beneficiaries of deceased members and deceased retirees who are currently receiving survivor benefits if the effective date of retirement or death for the deceased member or retiree was prior to October 1, 2004, for purposes of receiving benefits from the Employees’ Retirement System shall receive a cost-of-living adjustment (COLA) of four percent of the current gross benefit. In no case shall the COLA be less than fifteen dollars ($15) per month. The benefits provided in this section are limited to those retirees whose participation in the Employees’ Retirement System was based on Section 36-27-6, and whose employer at the time of retirement was a local board of education or a state-supported institution of higher education. The benefits granted in this section shall not apply to any other participants in the Employees’ Retirement System.