Definitely a speaker test- I can hear 15 with headphones, 14 with speakers. Not at all surprised at this tbh, rather than hoarding my hearing and wasting it on listening to people, I’ve spent it on rock and roll and motorbikes
17 with AKG headphones, 15 with Grado headphones, 14 with Monitor Audio speakers. It confirms my tinnitus is at around 12, probably due to years of motorsport, power tools and concerts. I use -20db ear plugs for music now except when responsible for the mix, that results in ringing ears for a few hours.