I can confidently predict that no, you won't make 15-20 percent as a long term average, though you may well manage a number of good years in a row. Save while the going is good.
So in summary: it is too complex to understand, unless you have a very advanced education in the statistical techniques they use to build the models.
(For example I don't have a PHD in physics but a few years of reading and following up on linear algebra, and I can hold my own in a conversation on sting theory with with a PHD Physicist).
These guys certainly knew their stuff, and they also had a system: http://en.wikipedia.org/wiki/Long-Term_Capital_Management