I'm pretty sure that what happened to me was an exception or a bug or certainly innexperience over Ethereum. I will establish all the facts in order to find what happened or at least an explanation.
Rigth now I know that was impossible to mine 15 ethers in less than 48hs with CPU. But I also know that I saw (I even have screenshots) with my own eyes those 15 ethers in my wallet, until I get an error with Eth Wallet and everything goes bad :)
At first my wallet started with 0 ethers and geth started from scracth to synchronize blockchain.
My question is very simple. What happened? I know that was impossible to get that amount of ether in so few hours, but how is possible that I saw those ethers?