How did you improve beyond 1500?

Practice when a young student I played at recess after School and lunch also played standard games on Fics ICC and Chess Net 25.0, 35.0,45.0,60.0 from 4:00 PM to 2:00 AM against all comers.

Played in School Tournaments Echecs et Mathes in Montreal whenever I got the chance to play

Correspondence Chess played Postal Chess (with cards)
and turned based Chess games on servers against good players 1750-2050 for years lost lots of games but won alot too.

When I was a teenager borrowed all the books at the city library most were from the 1960's and 1970's read them all. I solved the problems in Fred Reinfeld's 1001 Brilliant ways to Checkmate and 1001 Chess Sacrifices and Combinations this book helped improve my board vision with constant practice.

I played over tons of Master games on a chess set from books which helped me too.

There are many ways to be 1500. It is not a linear progression. Just getting your move selection method disciplined and efficient would boost you a lot. Focusing solely on tactics too. But that doesn't mean you "moved up" and it doesn't mean that finding the "right" (easiest?) way to hit 1500 is really what you want. Aim for love of chess and long term growth.

The rating number should help you get fair matches and if it gets stuck for a long time it could be a sign you aren't growing. But not every way of hitting 1500 is the same. Not every 1500 is equally close to 1600. You know what I mean?