That's a great booster alright. I'd say the 1.5lbs is probably more likely what it will be like going forward now. A lot of people lose water weight etc in the first week if you haven't been drinking a lot of water anyway. Before I started WW I would have drank about 2 litres or more of water a day anyway, love the stuff (haha) so I had no water loss in my first week.
But even saying that 6lb is a lot for someone of your weight so a good chunk of that would probably have been actual fat loss too, which is always great!
Plus you got your first silver 7!!!