Section 515 - Optional retirement programa. Any optional retirement program authorized by state law which, on the day before the effective date of this article, would be available to an eligible employee subject to the provisions of article eleven in lieu of joining a public retirement system of the state, will continue to be available to eligible employees subject to this article during the period this article is in effect.c. Nothing herein contained shall be construed as permitting an employee who previously elected coverage under an optional retirement program to elect coverage under a public retirement system of the state.N.Y. Retire. and Soc. Sec. Law § 515