That’s not possible. The chip used in that model was limited to 16GB. I worked in IT at that time and DB admins begging me to get them a 15” at that time with 32GB of RAM. I told them the chip from Intel was the limiting factor. When Apple updated a year or two ago, they moved to the next version of the chip which allowed 32GB. So yeah, 32GB in 2015 was not possible.