Sec. 15. (a) Except as provided in subsections (c), (d), and (e), a participant's employer shall make contributions annually to the account on behalf of the participant sufficient to provide the benefit described in section 17 of this chapter. For a participant meeting the eligibility rules set forth in section 17 of this chapter, the amount credited to the participant's subaccount balance shall be the sum of annual contributions and earnings for each year of service. The amount of the contribution each fiscal year must equal or exceed the following, based on the participant's age on the last day of the calendar year that is in the fiscal year in which the contribution is made: