I'm also in Singapore but don't have these issues. I'm with TDA. The worse is when I get a few seconds delay viewing charts when I toggle between stocks in my list. Then again, I'm not concerned with speed execution as I trade stocks over weeks.
I do care about latency when I play video games though! VPNs are useful only in that you have more options to route your IP to the end server. Sometimes I get a better ping with one or another, but probably nothing that would be obvious for trading. When gaming, anything over 220 is unplayable. Depending on time of day it's not unusual to get pings of 210 to 350.
I have TDA account as well. They definitely lag. Try to observe the opening. If you don't read the level 2 and tape, you won't know the huge difference.