For a beginner or intermidiate player openings are not very importhant for only one simple reason. They say don't memorize, know the idea. But how can a low rated player know the idea even if the opening goes exacly as he planned to (no side lines) if he blunder pieces to simple tactics. He can't create harmony with his pieces and are often blocked by pawns or simply can't make attacking plan... He is often lost and have no clue what to do , no matter his first 5-6 moves are in his memory but then following two are not.. study tactics is the fastest way to improve even way above 1500.
You have to know only opening principles and well known traps. But don't try to play for traps. understand very basic plans with different pawn structures like karo-can (black is solid but often passive) /french (black have bad light squared bishop but can create counter play) and thats absolutely enough for you. I did not know any of that and was already close to 1500. Everyone can reach 1500 if he simply dont blunder pieces.
You can also choose openings that don't really need to be known per heart. I learnt the English opening, but nobody play then main variations. I finally learnt this opening playing it, and playing it. Under 2200, you can play without knowing a lot of theory. Or choose an original opening: you will know as theory as your opponent.