I have tracked the OTB rating development of strong players in my city.
Strong players (who reached 2200 or higher) reached Class A (1800-1999) in one or two years, Expert (2000-2199) in two to four years, and Master (2200+) in four to seven years. These numbers reflect their advancement after starting rated tournament play They may have had practice and instruction before that.
In general, the ones who reached the higher levels tended to make more rapid gains early in their development. For example, a player who became an IM reached the 2200 level within three years. The Masters who reached the 2300 level tended to make faster progress than those who reached the 2200 level.
it is important to note that online blitz ratings are much higher than classical OTB ratings. So, we should expect to see different results on chess.com.
Players who peak at lower levels show similar learning curves that simply are less steep than those of Masters. They show less rapid early development, slower improvements over time, and they simply plateau at lower levels.
As a comparison, even for the most amazing kid wonders, like Magnus Carlsen or Judit Polgar it took years to get from complete beginner to 1500. Years.
I find it unbelievable that someone can do it 2 and a half months. So I don't believe it.
I don´t understand why its that unbelievable. it dosen´t take a genius to be 1500. It took me 6 months and i´m not even talented. There are countless stories online of people reaching 2000 elo in a year or 1800 FIDE in a year. My friend who became 1500 chess.com rapid in 2 and a half months is now 1980 fide after learning chess a year ago. I think you don´t understand how bad 1500s are, even 1500 FIDE is pretty bad so with dedicaton it´s easy to hit it quickly. Also, my account is proof that this type of progress is possible. @magipi