15. The annual amount of a deferred pension under the Civil Service Superannuation Plan payment of which is anticipated under this Chapter shall be established as follows:(1) by computing that pension in the same manner as the pension granted under that plan;
(2) by reducing the amount obtained under paragraph 1, during the pension payment period, by 0.5% per month, computed for each month between the date of the officer’s retirement and the date of his sixty-fifth birthday or, in the case of a female officer, her sixtieth birthday; and
(3) by reducing the amount obtained under paragraph 2 by the amount obtained under the first paragraph of section 63.3 of the Act respecting the Civil Service Superannuation Plan (chapter R-12), with the latter amount being reduced, during the pension payment period, by 0.5% per month, computed for each month between the date of the officer’s retirement and the date of his sixty-fifth birthday.