Luckily I didn't wait till end of the day Pacific time, but registerred several earlier (1 payment ; more then 15 though at once, probalby adding 1 by 1) (not an enormous amount above that 15, but I'm glad I could particpate), and went to rest a bit afterwards, because I saw that I had to wait 15 minutes for an email to be sure. But I fell asleep and in the morning I checked my eamil. And it had succeeded.
But still... I only saw the promotion here very late, and only had 5 hours apparently to register domains.
I wish I'd known earlier about this (and the other) promotions.
I had already 1 domain there that I once bought earlier (a .online-domain). So I was in fact no real "new customer".
I'll have to get into a bit further, and see how good they are as registrar.