Sec. 15. REDUCTION OF BENEFITS AUTHORIZED IN CASE FUND IS DEPLETED. In the event said pension fund becomes seriously depleted, in the opinion of the pension board, said pension board may proportionately and temporarily reduce the benefits of all pensioners and beneficiaries, but such reductions shall thereafter be paid to such pensioners or beneficiaries as and when said fund is, in the opinion of the pension board, sufficiently re-established to do so.