+1 on dwinter
ditch the canister filter for sure its not doing you any good. seeing how you already have the 2 small skimmers i would keep them. I would set up a 20g long sump, make it a traditional setup, one end input, middle area, out put on other end. run a skimmer at both ends sandwiching live rock and a DSB with macro algae. run carbon bag in the input area and a filter sock.
or 86 that idea, just run both skimmers in the 15g sump, put a bag of carbon in there and call it a day
or 86 that idea and ditch the canister, ditch the skimmers and fill your sump up with LR sitting on a DSB and use a fliter sock to catch large debris