I would like to encrypt a file containing 15-16 password, so a really small file, which encryption offer the best security for little file?
Are you worried about security or speed of encryption (since the file size is small)?
A good choice would be AES, and if you have a relatively recent processor in your computer, chances are that it supports the AES-NI instruction set where the encryption happens in hardware and is magnitudes of order faster than doing it in software.
Choose a key size of 256 bits if you're looking for the highest possible security.
The fact that AES was even chosen to be implemented in the processors says a lot about its effectiveness and speed.
See A Stick Figure Guide to the Advanced Encryption Standard (AES) for information on the history of AES, comparison with other schemes and the explanation of the algorithm.
You can use a simple manual cipher like Caesar's cipher where you replace every alphabet/number with another alphabet/number after certain positions.