Can I know how old are you? (Update: er ... i assume you are 39?)
I am a little past your targeted quit-rat-race age. And I am already out of it. I don't have $1.5m and I don't count the value of my HDB in. But instead of what some people think, you don't need $5 million to retire in SG. It all depends on your inflow and outflow. Cut down on unnecessary spendings. And invest away a healthy portion of your deposits prudently.
While you work towards this goal, do also think about something to do after you quit. Don't laze at the beach everyday. For me, I am doing my own trading and investment; apart from doing what I like, the minute income generated helps to offset my daily expenses. The longer term equity investments contributes to some passive income.
For potential health issues, it is very hard to predict. Even if one is employed and then kenna a critical illness, that person later may still have to leave employment eventually cos too ill to work.
When I was still working, I consistently transfer $ from OA to SA until max out. Since cannot touch might as well let them compound at higher interest lor.
I am still soldiering on but so far I see it can be done. Important thing is don't have debts (besides small credit card O/S) when you quit.
Last thing: health is more important than $.