I wonder how does this business scale. $15 a month is not much for paying salary.
It also depends on how much messages you get though; I'm sure there's a few that will just chat all day to fill up a need for social contact, while others will just message a few times a month to keep up appearances. Of course, as 'girlfriend' you could (and probably should) do some flood control yourself (max x messages / day / person) to be able to keep up with as many clients as possible.