Much much lower actually. We use the same stress response for seeing a lion that we do to stress about making a mortgage payment. That's why we get ulcers and zebras don't
On top of that Homo sapiens also just had much more freetime and the median lifespans were actually not too far off from what they are today (~72 years[0]). Yes there was a huge dip in lifespans in (some) agricultural societies and when the industrial revolution started and there's definitely a lot of variation in difficulties faced but overall on average prehistoric peoples were healthier and much less stressed out than the average American is today. Also peoples that lived on islands and certain other ecosystems didn't really have to deal with predators at all. Predators are very unlikely to be the biggest source of stress in general as even the most dangerous of all predators, big cats, are very unlikely to attack a group of humans. As long as you're with your tribe you generally don't have much to fear.
[0] https://www.bbc.com/future/article/20181002-how-long-did-anc...
