15 gallon stocking ideas?

What is your water hardness? If you don't know you can find out on your water company website or look it up online by zip code.

Personally, i'm a massive fan of guppies. They are fun and easy to breed. They are gorgeous and tolerant to most things. I would recommend fancy guppies in particular, maybe start out with two males and 5-6 females as the population may grow. If changing the amount, make sure to always have 2-3 female guppies for every male if you mix genders. If you don't wish for breeding, I would recommend male guppies as they are usually more beautiful, brightly colored and longer fins. Freshwater shrimp are tolerant bottom-dwellers, I recommend around 4 shrimp. Personally I have ghost shrimp, but cherry shrimp or any other kind works well too! These animals get along well with most other creatures as long as they aren't able to be eaten.