Not sure why GM recommends 15W-50 for track. My brother used to work for GM Advanced Vehicle Engineering Lubricants Division and always told me 10W-40 is more than enough for track use, where some viscosity loss can be expected. Hot viscosity is about 60% higher than 5W-30
https://www.mobil.com/en/lubricants/...obil-1-15w-50/