This character is a Control and is commonly used, that is, in no specific script. The character is also known as NEGATIVE ACKNOWLEDGE.
The glyph is not a composition. It has no designated width in East Asian texts. In bidirectional text it acts as Boundary Neutral. When changing direction it is not mirrored. U+0015 prohibits a line break before it.
The Wikipedia has the following information about this codepoint:
In data networking, telecommunications, and computer buses, an acknowledgment (ACK) is a signal that is passed between communicating processes, computers, or devices to signify acknowledgment, or receipt of message, as part of a communications protocol. The negative-acknowledgement (NAK or NACK) is a signal that is sent to reject a previously received message or to indicate some kind of error. Acknowledgments and negative acknowledgments inform a sender of the receiver's state so that it can adjust its own state accordingly.
Many protocols contain checksums to verify the integrity of the payload and header. Checksums are used to detect data corruption. If a message is received with an invalid checksum (that is, the data received would have a different checksum than the message had), the receiver can know that some information was corrupted. Most often, when checksums are employed, a corrupted message received will either not be served an ACK signal, or will be served a NAK signal.