Is this employer-provided health care? Sounds like you're receiving is subsidized. Living on $18k a year would be rough. Are you splitting an apartment? How much would you be paying if you had kids and needed another bedroom? Again, context is key. For a single person in their 20s, who will have the lowest level of responsibility and statistically the best health situation of their life, it's possible. But for other people, $1.5k/mo in a HCOL would not cut it.
As in, I could make $25k (at a level where the tax rate is effectively near-0) and still save > $5k per year.