So here's the deal. Yes you did fail. Which is why you were seeing higher FC usage and therefore questioned whether your SWG was working. So that's progress on a few fronts since we know you have something going on algae-wise and that your cell is working. The FC level of 15 was not a full SLAM level so it's not crazy that it didn't fix it. It's an intermediate approach that often works for small problems. But it didn't in this case.
Next up is to determine your actual CYA level and then SLAM at that level. There are some keys to performing that test. Bright sunshine is required. Read it at waist level with your back to the sun, test tube in the shade. Add the solution to the tube up to a numbered line, then see if you can see the dot. Don't stare just glance in for the dot. You actually can still see it just a little/tiny bit when reading it correctly. If you still see it well, add solution up to the next numbered line and look again. You can pour the solution back into the squeeze bottle and do it over as many times as you like to test your consistency. It is the hardest test to be comfortable with but practice does help. Come up with your CYA number then use the FC/CYA chart to determine your SLAM level.
SLAM level will be between 20 and 31 if you CYA is from 50-80. See here...
FC/CYA chart
You will want to follow the SLAM procedures to the letter. Making sure to lower pH per the instructions before the test because pH levels are invalid above 10 (which you already are so I'd let it slide down to 10 to test the pH and adjust, then start the SLAM). It shouldn't take long to lower FC since you are using decent amounts of FC.
SLAM instructions
General algae discussion
One other thing to be doing is brushing regularly though I don't think surface algae is your issue. You could have something in the light niches or any other place that water doesn't want to circulate well. I'm not familiar with opening light niches on liner pools but I think it's the same as a gunite. You will unscrew one screw and the light pops out to reveal the already flooded niche - this is where algae could be and would need scrubbing (not highly likely since your pool is "kind of" new. Let's see if someone will confirm. If not, I'll get that confirmed. And it could also be the pipe gunk as we were suspecting.
Only two things consume FC, algae/bacteria/contaminants and sunlight. Rest assured that your pool isn't special and you've eliminated sunlight from the equation with the OCLT test and it still failed - so we know what the issue is. Can't say how many days it will take but it will solve the problem but a SLAM is the resolution.
You will want to turn off your SWG for the duration of the SLAM and using strictly bleach or liquid pool shock (bleach but at higher concentrations).
