It depends what your objective is. If you want to do something more that just the 150/155 sequence then 155 will probably be better for you because from my understanding if you do 150 you end up having to take a 3rd class for a math major minor. If this is just to fill an MNS credit then 150 will be fine. If there is a pre-req for another class (econ stats) 150 will also be fine. My understanding is that 155 is mostly for engineering students or math students, and there is little reason to take it if you aren’t one of those two. A lot of the differences between 150 and 155 are not necessarily due to the class in particular, but the professor that you take, this is going to be true of every class.