What does Genesis 31:15 mean?

Rachel and Leah are telling Jacob why they will support him in the move away from their father and homeland to travel to live among his people in Canaan. For one thing, they don't believe they have any future inheritance coming from their father.

Now they express that they, too, feel they've been mistreated by Laban. It's not immediately clear why they say that he has treated them as foreigners, though it might mean he was distant or cold to them once they were married to Jacob (Genesis 29:20–28). It's possible they are identifying with Jacob. Their father claimed him as family but then mistreated him as one would a foreigner. In the process, he mistreated his own daughters, as well (Genesis 30:31–43).

On the other hand, it's not hard to understand what the women mean—that their father sold them and devoured their money. Laban used trickery and his daughter's marriages to get 14 years of labor out of Jacob. That was good for Laban, but it also meant withholding money from his own daughters and grandchildren. The two sisters had been married to a man who became an indentured servant, a kind of property, belonging to Laban. In that sense, they were sold into slavery, as well, to their own father. Apparently, any money paid to a father by a bridegroom would customarily be saved and given to the bride in the inheritance when the father died. Jacob's only dowry was his service, so there was no money waiting for Rachel and Leah when their father died. He had already "devoured" it all in using up Jacob's work for him.

Further, Laban's most recent attempt to cheat Jacob meant yet another moment where the interests of Laban's own daughters came second to his greed. Despite Leah and Rachel's intense rivalry (Genesis 30:8), they are in agreement on this issue.