Whenever I have joined SW, my home scales have always, without exception, weighed exactly the same as the class ones. I am a constant weigher and used to weigh myself before I went to class...I don't like surprises!!
I still went to class though as I wasn't going just to be weighed but for the group support also. These days I don't need the support, I can do it on my own, its taken years of dieting though I have to admit. My point is though, if your scales differ from one week to the next I would suggest that your scales are not that accurate? As already said, SW scales are more likely to be right than any home scales. Yes, there have been rare incidences where the SW scales have been wrong but that was only found out when lots of people in a class had a problem with their results one week. I think maybe you need to think about why you attend a group, for the support or the weigh in or both and the decide. Don't forget also.....1.5 lbs is still a great loss....WELL DONE!