It means for 15-30 dollars a day you would need to be a magician, of course you can make that much money some days but there will be days where you lose that much money and maybe even more, however if you hang in there and continue there is a chance of making profit in the long term.
Yes, making of $15 to $30 will be possible after having long experience with crypto trading but definitely not in the beginning days itself. Only with the help of some miracle, some people may get that much profits on daily basis but the actual is mixing of profits and losses happening for most of the traders. People are not ready to focus on learning and becoming a professional trader but they are simply targeting how much profit they want to have on everyday. Trading is not simple as we do dreaming.
Everything is possible but in this situation trying is better than waiting. Meaning I suggest you to try because we don't know how good you are and the only person who know is you.
But should not trade blindly. Even for trying, he should prepare himself so that he will be capable of handling the situation better. Even for trying, some people are losing big money and I do not want that to happen for OP too.