first off, 15 gals seems a lil small for 11 fish. but before i say anything more without knowing what im talking about, what kind of fish are they? you seem knowledgable about the causes of algae, and you are able to keep the algae off the tank walls
for the algae on the bottom of the tank and the algae rolling around, i would suggest buying a few shrimp, if the current fish will not eat them (like my puffer! haha) they'll clean up your tank just like jacque in finding nemo. and depending on the type and size of your fish, maybe a very small pleco. though i do worry it maybe a little crowded for one. good luck with your algae!