I'm sure the translator tried but I agree with you. There's too much missing.
more accurate translation chap15 : https://drive.google.com/drive/folders/0B4NmCaOXmOzvVmdOb3U4aUl3T0U
That's because the translator is using the spanish translator to make these. (You can notice it when this duet girl writes a SMS to Sangwoo) Since the spanish translations generally suck, that affects the english. Is not our translator fault :)
*the spanish translations to make these
the translations is somewhat a bit off, too many wrong translations.