Current stable version is 15.44 - Released May 26, 2022.
As most of the Meraki devices are running on this version, this is showing as stable version.
Stable firmware version is decided by firmware version that is running in most % of Meraki devices (based on millions of devices).If the number of meraki devices are running the firmware version 16.16 or 17.xx is higher , then these will be notified as stable version.
Every time updated firmware versions are notified to Meraki organization from backend, we can check the release notes and decides if we want to have that improvement or not. If we don't want it, we can certainly reject it and we will be never prompted for that firmware upgrade. When next firmware release is done, we may or may not get the prompt for firmware upgrade and we can cancel it if required.