With some handling he may or may not calm down - most balls are very docile - some are aren't. 15 days really isn't enough time to tell - for starters once you bring the snake home you should not handle it until it settles into it's new home then gradually increase the amount of time that you handle it. I know easier said than done. It could be perfectly good snake but for the next 15 days it could continue striking just because it is stressed from the move and handling. My suggestion is first see if you can get that 15 day period extended due to the circumstance - then let the snake settle in for a week don't disturb it except to change water clean cage, etc. - after the first week - you can feed it and handle it for like 10 minutes a day. If it eats and you are comfortable enough to keep it go for it - if not take it back.
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Tosha 
"Nihil facimus sed id bene facimus"
7.33.0 Ball Python (Harry and Fluffy and gang)
1.0.0 Angolan Python (Anakin Skywalker)
0.0.1 Green Tree Python (Verdi - yeah I know but my kids love the book)
0.2.0 Feline (Pippen and Pandora)
0.0.1 Desert Tortoise (Pope John Paul aka JP )
2.2.1 Fish (1,2,3,4)
0.0.2 frogs rescued from pool skimmer