This will depend upon your age and the circumstances in which you are leaving the Fire & Rescue Service (FRS). Your Normal Pension Age (NPA) in the FPS 2015 is 60, but if you remain an active member, you can continue to accrue pension (and would get an 'age addition' to reflect the fact that you have postponed receipt of your pension). There is NO limit to the amount of pension that you can build up by remaining in service.
You may request payment of your pension before age 60, provided that you have reached age 55 (your minimum pension age), but it may be reduced to reflect early payment. Or, if at any age before reaching age 60, you become incapable of performing any of the duties of your role, you may be entitled to an ill-health award.
If you have left the FPS 2015, with at least 3 months' qualifying service (or have had a transfer value paid into your pension account from another occupational pension scheme), you will have become a deferred member of the Scheme. In this case, you will become eligible to draw your deferred pension at your 'Deferred Pension Age', which is linked to your State Pension Age (SPA) and may therefore change in the future, or at age 65 if higher.
If you wish, you could give written notice to the FRS that you would like to receive your deferred pension at or after age 55 and before Deferred Pension Age. In these circumstances, however, the pension would be subject to an early retirement reduction based on factors provided by the Scheme Actuary.
Or, if before reaching Deferred Pension Age, you suffer from ill-health to the extent that you would be incapable of undertaking regular employment and this incapacity will continue, at least, until Deferred Pension Age, you could request early payment of the deferred pension on ill-health grounds. The decision as to entitlement would be made by the FRS after they have considered the written opinion of an Independent Qualified Medical Practitioner.