YOU SAID:
Cats sleep for 15 hours a day.
INTO JAPANESE
猫は1日15時間寝ます。
BACK INTO ENGLISH
The cat sleeps 15 hours a day.
INTO JAPANESE
猫は1日15時間眠ります。
BACK INTO ENGLISH
The cat sleeps 15 hours a day.
That didn't even make that much sense in English.