Well, you write well, have a nice / growing resume, and you’ve got great momentum. So, all things point to higher earnings in 2019! If you’re still doing *anything* in NYC for less than, say, $15–20/hour, that’s probably what you ought to jettison first (IMHO). Freelance-wise, up your minimum rate a bit for 2019. If $25/hour is doable for you (which it wounds like it is), I’d say start there (or even higher, depending on the work you do). But, I think content writing s/b a higher-paying line of work. Most of that goes through marketing or PR departments, which have decent budgets and won’t flinch at 2x the rates you’ve mentioned, in most cases. (Much more, in others.)
The way I did it was to start out at like $20/hour… and then I’d immediately go for $30/hour gigs (or more), and I kept doing that over and over, slowly churning clients over several years until my lowest-paying ones were way, way, above where I started. At some point, what happens is that you kind of find the ceiling. That’s the sweet spot — getting all (or most) of your clients grouped there.
One other note is that, sometimes, when you charge more, you’re seen as more valuable. And vice-versa. So, if your rates are too low, some people might not think you’re experienced enough.