Almost all crypto on downtrend since january untill now so we have very little chance to make profit. To avoid loss is better we short the price by trading in margin trading platform.
It depends on you most of the time as well as your style of trading, but since January till date, there have been some opportunities in between, both for short term traders as well as midterm traders. 15% per day though is something that is never guaranteed as that would depend on the nature of the market and your own pattern or style of trading, but in most cases, for short term traders and in good market conditions, you can at least get something related in a week. Basically, you have to consider money and risk management when you are looking at 15% per day of your total trading account, which may not sound too plausible.
Don't believe me start with 10k and increase your gains by 1% a day, you will see it grow very quickly.
I understand that you are referring like 1% in $10k is equal to 10% in $1k. You must be right. Yes, instead of trying more profits out of small capital, in some sense your idea sounds good. But, here we need to also consider veteran people's suggestion of risking small capital as losing entire capital while trading is 101% very much possible and a most common one too.