I'm currently 18 years old, non-smoker. Should I take up Pruflexi Cash endowment plan? (15 years) ?

Fact of life, one does not mix insurance with investment, due to the high cost of premiums for low insurance coverage and mediocre/negative returns.

You're young and can take a lot more risk with your investments. An endowment policy is a conservative portfolio that will give you about 2-3+% with flexibility of coupons during your savings period.

But with your investment horizon, you could take the risk of a 100% globally diversified equity portfolio. You may want to introduce endowment plans in your 30s and 40s when you start introducing bonds and fixed income instruments to your portfolio.