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.

Now you should not sell them anymore. Our market will not go down much more. This is where the price of all altcoins will grow again but it will be slow growth.
So we need more patience to achieve success in the future.