Or HaChaim on Genesis 45:15/אור החיים על בראשית מ״ה:ט״ו

1ויבך עליהם, He cried over them, etc. After the brothers observed Joseph crying over them they were able to respond to him and they said to him whatever was on their minds. After all, everything that Joseph had said to them up to that point might have been designed only to alleviate the brothers' feeling ashamed of their conduct. It was only after he kissed them and wept over the years they had been separate that the brothers recognised Joseph's truly good character and that he was a true brother that they were able to speak to him naturally. Whereas Joseph's original burst of weeping could have been attributed to his reunion with Benjamin, the latest burst of weeping definitely concerned his reunion with all of them.