16V is fine for C1 and C3 and may be OK for C2 if you can always guarantee that the input voltage to the 5V regulator will be less than 16V. Capacitor derating, even for defence high reliability requirements, usually means a derating factor of around 30 to 50% on the voltage rating, although it's temperature dependent to some degree. For hobby purposes going to within 10% of the max rating is usually absolutely OK.
[Edited to add that this reply crossed with the one above - we must have been typing together!]