Better question: What kind of kid who at least *thinks* he might be capable of hacking the school's system wouldnt be aware of cloud storage/backup? Clearly setting a fire would do nothing to cloud stored data.
In the western world we know that children think and reason differently, don't oversee all consequences of their actions, and because of that we try them differently, in juvenile court. A 15 year old who did not perform on a test, panics and does something stupid. Panic means: no reasoning, no oversight, and the existence of backups is totally forgotten, even if he knows about it.
In the US there is a tendency to try more children as adults, especially when the crime is big, like murder. This is the general tendency resulting from rage and frustration when people are not satisfied with their own situation, and they need someone to blame. They need a black sheep.
This is not a big crime. If the school burnt down, if someone died, that would have been something else. It could have, but it didn't. It's the same when you stab someone with a knife. If two people do this to two victims, stab them in a similar way, and one dies, the other not, the sentences will be different, although intentions and acts in this (imaginative) case are similar.
Nobody was hurt, the next day it was business as usual. So give this kid a reasonable sentence for the damage done, and let him have a chance to see his error and learn from it. The lesson should be that he was lucky that this didn't turn into something really big. Next time his luck may change, and this experience may hold him back then. Send him to prison for seven years and he will come out as a wreck or as a professional criminal. Who wants that?