I did 4 consecutive online reports before they took the whole system off line last year. After I read it that it came online again a few months ago I tried again both for myself and my wife, no luck this time but I have read that others were successful in Chiang Mai. For me reporting via snail mail is a better option.
Tried again 3 weeks ago in Chiang Mai, still pending, so send in by post and that works flawless so far. I got my passport slip delivered back home within a few days.
you are right passport holders of Korea, Brazil, Peru, Argentina and Chile will get 90 days in both airport and land border. I don't know any that get only 15 days visa exempt entry.