That's the wrong kind of thinking ... you should really be more optimistic. Do you feel prepared for the LSAT?
That said, Native Americans tend to get the biggest boost in LSAT; I've read that it's from 7-10 points. So, in theory your 155 would be like a 162-5. Yet, this is not set in stone. It's not automatic. If you get a 155, that does not necessarily mean you should expect to get into a school such as Boston University or Texas, where the 25th percentile LSAT is around 162 or so. For your example, UC-Hastings, if I were in your position, I would feel like I needed around a 158 or 159 to stand a decent chance of getting in.
A score in the 150s with your GPA is good enough for many of the Top 100 schools, regardless of your background. If you were looking to go to a very top school, such as Michigan, you would definitely need a score in the low 160s, at least. But for the majority of tier 1 schools, if you can get a score in the high 150s you can probably go to a lot, but not all Tier 1 schools. Below 150, I could not say with any certainty that you would be accepted by any law school.
Moreover, you will need to show the admissions committee how you've not just overcome the disadvantages that come with a poor background, but that you've thrived. It will not be readily apparent from the boxes you check off on your applications.