YOU SAID:
I went to the supermarket and bought fifteen pounds of potatoes
INTO JAPANESE
私はスーパーに行き、15ポンドのジャガイモを買いました
BACK INTO ENGLISH
I went to the supermarket and bought a 15 pound potato
INTO JAPANESE
スーパーに行って15ポンドのジャガイモを買いました
BACK INTO ENGLISH
I went to the supermarket and bought a 15 pound potato
That didn't even make that much sense in English.