Simplify the following text for a Grade 6 native English-speaking person.
Original: The key signatures with seven flats and seven sharps are rarely used because they have simpler enharmonic equivalents . For example , the key of C major ( seven sharps ) is more simply represented as D major ( five flats ) .
Simplified: There are fifteen possible key signatures : up to seven sharps , up to seven flats , or no sharps or flats .