During the last week I bought coins and they almost immediately fell by 10-15%, and today early in the morning I saw how they fell by another 15-20%. How long will it last?., and whether I should sell for what I have. I wouldn't want to be left with empty pockets. 
No one knows, we can speculate and give various dates but that is far away from knowing anything at all. It is your money and you are only one who can and will make this decision. What alt coin do you hold and what amount or is this hypothetical question?