You don't need to upgrade the bootstrap/bootroms on a 2500.
Usually, it's recommanded to sync the bootimage with the main image (ie if you have 12.1(5) as the main image you should also use a 12.1(5) boot image). This is not the case for 25xx where bootimages are on a bootrom and are not meant to be synced with the main ios running on the router.
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...