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?
5 years from now is a pretty long time. a lots of things could happen in that period.
Furthermore it would be 2 years after the next halving, which is happening in summer 2020.
IF Bitcoin should still perform as it did since it's creation, $15000 is definitely possible.Probably more!
But there will be many more attempts to take over Bitcoin by bad actors, as we see going on now (NYA SegWit2x BTC1). And also huge and extreme FUD, just to separate the scared people and weak hands from their coins.