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Cisco often maintains several software version trains, concurrently. So it's possible you'll see an older IOS version with a more recent release date than a newer IOS version.
Technically, if the platform supports it, you can move up and down versions (same feature set). Legally, to move to newer versions, you need an active maintenance contract. Not sure about moving down, if you don't have a contract.
If you have an IPBase license, the IPBase image has a slightly smaller footprint, but the IPBase license is also supported by the universal imsage. If you have an IPService license, installing IPBase image, I believe will work, but you'll lose IPService features. (Forgoing assumes you've configured the installed license for execution. If you have sufficient flash, you can install multiple images, different versions and/or feature set. You can also configure to boot into different images.)
I would use 15.0.2-SE9 since it is a gold star release.
The software you are looking at is "trains". Trains are individually updated, usually to resolve bugs. New trains are created to support new hardware (such as modules) or new features. They are created as separate trains so that bugs don't affect users who don't have the new hardware or need the new software features. After a while the trains get merged back into the main maintenance release.
So lets say you were running 12.2.58-SE1 at the moment. Lets say you don't need to support new hardware, don't need any new software features, but are interested in bug fixes. Then you would consider going to 12.2.55-SE10. Because it contains nothing new, only bug fixes, it should be super stable compared to what you have now.
Your licences should remain the same when upgrading. You should stick to using the same type of image you have now. If it is "ipbase" stick to "ipbase". If it is "universal" stick with "universal".