What should I invest in as a 19 y/o with 15k savings + side income of 1k+ monthly? ?

I would reconsider the Nikko AM SG STI ETF as the STI is technically an index is is highly skewered towards SG banks. A better option would be roboadvisors. Being young, you can also consider putting some money into more risker instruments such as P2P lending and cryptocurrency stablecoin lending(Look into Blockfi, Dai, Celcius)

Woahhh 19 with 15k savings +1k side income monthly, that's impressive! You should pat yourself on the back! I'm your age as well and I just started investing not too long ago!

It all comes down to your risk appetite, for me i dove right into individual stocks, went for REITs, Blue Chips, etc. Firstly find out whats your risk appetite! If you have a low risk appetite then something safe like Singapore Savings Bond (SSB) or STI ETFs would be pretty good since in the long term you'll be gaining decent returns. Robo advisors are also great since it's similar to your DBS RSP, but you'll be vested in the global markets like US etc. rather than just in Singapore. I'd say Stashaway is pretty good, since you can optimize your portfolio according to your risk appetite!

If you like a challenge, I'd say learn how to stock pick, don't think too much into it. Many people assume, "Oh I need to have a big capital to start" or "Oh I don't know how to choose". Firstly, I started out with 2k capital sooo don't worry about the capital since you have 15k to play with. Secondly, the internet is full of helpful information and it's all free! I learnt everything from videos and reading articles etc. Also there is a misconception that you must pick 30-50 stocks, but trust me, being invested in 10-20 is more than enough !!

Good luck in your investing journey and for school as well !