Sec. 15. INCREASE IN BENEFITS. (a) In addition to the postretirement increases under Section 10(h) of this Act, the pension board may increase annuities payable under this Act by an amount that does not exceed the annual increase in the amount of premiums being paid under a group insurance program provided for retirees of the city.

(b) The pension board may distribute a supplemental payment to all retirees and eligible survivors who are receiving annuities as of January 1 of the year in which the supplemental payment is made. The supplemental payment shall be credited to DROP participants who are participating in DROP as of January 1 of the year in which the supplemental payment is made, if the pension board's actuary determines that as of the end of any fiscal year:

(1) the value of the pension system's assets exceeds the amount of the pension system's accrued liability;

(2) the pension system has met the actuarial investment assumption for the previous fiscal year; and

(3) the issuance of the supplemental check will not cause the city's contribution rate to increase.

(c) A person may not receive more than one supplemental payment as a result of the person's status as:

(1) a retiree and eligible survivor; or

(2) a DROP participant and eligible survivor.

(d) A pension benefit or allowance provided by this article may be increased if:

(1) a qualified actuary selected by the pension board determines that the increase cannot reasonably be considered to jeopardize the pension system's ability to pay any existing benefit;

(2) the increase is approved by the pension board and the city in a written agreement as provided by Section 3(n) of this article; and

(3) the increase does not deprive a member or retiree, without the written consent of the member or retiree, from receiving the immediate or deferred retirement benefit that the member or retiree was eligible to receive under this article before the increase.