The 15 hours is how long Apple estimates the shuffle will play music, in typical use, from full charge to empty. That's 15 hours of playing time, not counting the time it is not being used, with the understanding that batteries do drain slowly and lose power just by sitting there.
You can also charge it from a power adapter, like this one
Other chargers that have a USB port may also work. However, if there is no computer, there is no way to load it with music. If you are going to load it with music for him, and make ongoing updates (and you have a computer that can run iTunes), that would work.
You can use any external self-powered speakers that connect with a standard mini-stereo plug.
The ideal simplified use for an iPod shuffle is to play songs from it in random ("shuffled") order. Turn it on, play songs in no particular order, turn it off. You can do more with it, but that will require doing things like setting up and syncing playlists, and switching playlist using the VoiceOver feature,