There are 15 keys
For the major and natural minor keys, there are 15 standard key signatures, each representing a different starting note or tonic. Using the rule of seven, these 15 key signatures are:
0-7
C major/A minor (no sharps or flats)
C# major/A# minor (7 sharps – F#, C#, G#, D#, A#, E#, and B#)
Cb major/Ab minor (7 flats – Bb, Eb, Ab, Db, Gb, Cb, and Fb)
1-6
G major/E minor (1 sharp – F#)
Gb major/Eb minor (6 flats – Bb, Eb, Ab, Db, Gb, and Cb)
F major/D minor (1 flat – Bb)
F# major/D# minor (6 sharps – F#, C#, G#, D#, A#, and E#)
2-5
D major/B minor (2 sharps – F# and C#)
Db major/Bb minor (5 flats – Bb, Eb, Ab, Db, and Gb)
Bb major/G minor (2 flats – Bb and Eb)
B major/G# minor (5 sharps – F#, C#, G#, D#, and A#)3-4
3-4
A major/F# minor (3 sharps – F#, C#, and G#)
Ab major/F minor (4 flats – Bb, Eb, Ab, and Db)
Eb major/C minor (3 flats – Bb, Eb, and Ab)
E major/C# minor (4 sharps – F#, C#, G#, and D#)