>>. E.g. check out Harvard: their "low" 15.4% on their endowment fund
A great example of the thinking that has decimated many public and private pension plans.
They use the results of a couple of boom years and forecast them into the future, neglecting to note that for several prior years there might have been negative returns.
The probably that the returns of the past couple of years will be repeated over any meaningful period are slim.