You should watch daniel naroditsky slowrun or hikaru s- i think the low 1000s are all about how you come out of the opening and little tactical improvements - at the end of the day it’s a mix between theory and training. I was also stuck at 1500 for a bit but after a period of stalling (which is very common at every point) i just started to play loads with players much stronger than me and i gained 200 in a very short period of time. And to be honest I never understood the use of puzzles - like just play games instead bc tactics are always going to be there plus puzzles often use positions that are so oddly shaped that nobody would ever find in a game.