If I buy just 5 bitcoin today 2500$, Next 5 years bitcoin will be 15000$
this is the way that I should invest or not?
Well, for me it is good idea. You should buy bitcoins now until its price is not that big enough because there's a possibility that the every year will pass bitcoins price will goes up too. Furthermore, I do believe that if you invest your money on bitcoin and wait for the right time to sell you could guarantee that you will get a high profit.