my 15 gallon started off as a caribbean tank, I kept it "caribbean" for a year. I stopped maintaining caribbean only animals because of the rarity of caribbean livestock where I live.
But I kept royal gramma, chalk bass, clingfish, sharknose goby, neon goby, yellow head jawfish, caribbean hermit crabs, some types of turbo snails. RFA's are also from Caribbean so I have several of those.
But very few corals originate from Caribbean (again, due to where I live). So it was a challenge to fill up empty spaces in the tank.
I had to research everything before putting it into my tank, to make sure it was Caribbean origin, so I really learned a lot in that year.
And of course a 15 gallon tank is very small. Several larger fish originate from the Caribbean such as hogfish, tangs, Triggerfish and Angelfish, etc.... but you need the tank size for it.
So due to my small tank size and availability of livestock where I am, I found it challenging to stock a 15 gallon with Caribbean only.
Anyway, hope it different and easier for you. Good luck.