If you choose 15 alts, it is better to choose them from the top 100 markets, because if you look for coins that are in the middle of the market, you can get to the scam
The most important thing is how the investments will be distributed, what share each cryptocurrency will occupy, how many parts the capital will be divided into. To get a noticeable profit, you will have to periodically sell and buy cryptocurrencies, changing the composition of the portfolio depending on the situation on the market. However, it is really better to pay attention to the top-rated cryptos.