After termination from service and upon application for service retirement, the service retirement benefit must be as follows:
(1) for members not covered under 19-5-901 or 19-5-902, 3 1/3% a year of the member's current salary for the first 15 years of service credit and 1.785% a year for each year of service credit after 15 years; or
(2) for members covered under 19-5-901 or 19-5-902, the benefit provided under subsection (1) except that the benefit must be calculated using highest average compensation.