Brazil is beautiful from what I've heard, and I'm shocked that the cost of living is that low. OP, there's nowhere in the US where you can get a meal as cheap as the one you described (am I correct in assuming that's USD in your post?).
Yes, all the values I post are converted to USD, taking the currently Real : Dollar ratio on the moment I'm writing the post.
Even the dollar menu at McDonald's is now like the $5 menu, and if you can easily spend $15 just for an unsatisfying sandwich, fries, and a watered down soda. It's no better anywhere else as far as I know, and I think it's only going to get worse. There's an egg shortage now? WTF?
Years ago McDonalds had some very interesting promotions here. Each day of the week we had one sandwich in promo, including Big Mac. I think it was about 2$ on that time, and Dollar was also cheaper compared to Real. I remember buying a sandwich and a big fries portion and taking home, so I had coca-cola cheaper from the supermarket.
But since then, I haven't been to big centers often anymore. Just last year when I had the opportunity to return to McDonalds, I saw that promotion didn't exist anymore. Now prices are also more expensive and similar to the 15$ you mentioned, although I remember eating a lot. I'm checking the prices on the internet right now and it says a Big Mac combo is around 5,33$ (probably with a medium portion of fries and soda, which are small for my taste).
Going much back in time yet, there was also a vanilla ice cream cone promotion, on which you received a free one after 5 bought (could be acquired in different days).
I read on an article where minimum wage in Brazil is 2265 BRL/Month or $440/Month [1], how it's possible you're saying the minimum wage is only $25/Month.
Then read it again, and I never said minimum wage here is 25$ monthly...
These rates aren't considering the raise to 1320 BRL this year, as announced by the president, so it's slightly higher (not that 18 BRL extra worth anything, anyway).