port - What is this 15 pins connector?

I do not think it's a serial port as there's too much pins. It's used to plug a very old controller. Will I be able to find any adapter to USB?

Answer

Will I be able to find any adapter to USB?

Yes

I do not think it's a serial port as there's too much pins. It's used to plug a very old controller.

It's a game port connector

The game port, originally introduced on the Game Control Adapter, is a

device port that was found on IBM PC compatible and other computer
systems throughout the 1980s and 1990s. It was the traditional
connector for joystick input, and occasionally MIDI devices, until
replaced by USB in the 21st century.

Source: Game Port