"10 to 15 years should be perfectly adequate. If it's going to make money, it'll either do it in the first year or two, or never."
One of the pains of the Google Book Settlement fracas has been listening to people who know nothing at all about the writing trade confidently spouting total rubbish.
i) Some of the books with the all-time biggest sales have been 'sleepers', gradually building popularity over many years through word of mouth. The Lord of the Rings is a case in point.
ii) It is likely to take at least 10 years for an author to achieve name recognition with the public: at which point his/her early books may finally start to make money
iii) Books can, and often do, go in and out of print over many years, earning their authors further welcome payments with each reprint
And let's say this loudly and clearly: most authors earn only very modest sums from their writing, and those amounts have been falling sharply in recent years. You want, out of ignorance and greed, to slash their incomes still further? Then look forward to a future in which your favourite mid-list writers - the ones who aren't top sellers, but steadily turn out books you enjoy reading - are driven out of full-time writing; maybe stop writing altogether.
Do you want a future in which your choice of new reading matter is confined to books 'by' celebrities, online fanfic, and Wikipedia articles? I assure you, it is a real possibility.