The annual increase (or decrease) to your 2015 Scheme future pension income for inflation (CPI the previous September) and Active Member Bonus (1.5% if still contributing to the 2015 Scheme).
Deferred pensions and pensions already being paid also increase in April each year by the Public Sector Pensions Increase (CPI the previous September). The first April after 1995 or 2008 Scheme pension payments start you get part of the increase – number of complete months of payments divided by 12.