YOU SAID:
It's their anniversary on Monday. They shall be married for 15 years, I think.
INTO JAPANESE
月曜日は彼らの記念日です。彼らは15年間結婚するだろうと私は思います。
BACK INTO ENGLISH
Monday is their anniversary. I think they will get married for 15 years.
INTO JAPANESE
月曜日は彼らの記念日です。彼らは15年間結婚すると思います。
BACK INTO ENGLISH
Monday is their anniversary. I think they will get married for 15 years.
That didn't even make that much sense in English.