Simplify the following text for a Grade 9 native English-speaking person.
Original: The Legend of Zelda : Spirit Tracks , released as Zelda no Densetsu : Daichi no Kiteki in Japan , is the fifteenth installment of Nintendo 's The Legend of Zelda series .
Simplified: The Legend of Zelda : Spirit Tracks , released as Zelda no Densetsu : Daichi no Kiteki in Japan , is the fifteenth game of Nintendo 's The Legend of Zelda series .