Usually they recommend you to diversify your investment, so you avoid losses.
But as a real approach, having $1.5k, would you invest in how many cryptocurrencies ?
What if I invest little by little, only in Bitcoin, would that work as well ?
Diversifying your investments is a way of investing to minimize your risk and losses. Investing little by little is known as cost averaging. Investing in bitcoin is a better choice for me since it is like the center of all cryptocurrencies as its price has a big effect on how the prices of other altcoins might be. Through cost averaging, you can avoid having big losses because you can balance out the amount of your investment if in case it goes down. Your aim is for long term investment anyway so there is a higher possibility that you will grow the value of your investment given the situation that mass adoption will continue.
I would invest 10% at a time in different alt coins, and keep a decent amount in bitcoin or ethereum to hold onto. That way you can account for more possibilities. If the price of something you bought drops, buy more of it so your cost average gets lower. Or if another project shows up with tons of promise, you still have some to invest. $1500 isn't a lot to work with, but diversifying is very very important.
This is also a good strategy. Altcoins has a tendency to grow more in value compared to bitcoin because their prices are not that significant yet. There are coins that has a lot of potential but it needs a lot of research before investing into altcoins. If I were you, I would go for altcoins that already has a track record of withstanding with time.