Otherwise, easy come may easy go.
That is what happens to many people's earnings here :)
I think 10-15 years enough. There should some time to stay that wealth.
That is pretty reasonable to build a steady income stream I believe. It is like building a business, the first few years, everything goes back into development and growth - after that a small living wage comes out with more going back and then finally, it is a bit smoother, with a larger wage possible, but plenty staying into develop further.