Reti opening

At 1500, I wouldn't recommend it. Too many pawn structures and too many openings to know. You cannot force 1...d5, and therefore cannot force the Reti.

Even if you do get the Reti (1.Nf3 d5 2.c4), you have to deal with 2...d4, 2...dxc4, 2...c6, 2...e6, etc, all leading to VASTLY DIFFERENT positions.

Then you have to deal with either the English, QP opening transpositions, or Reverse King's Indian positions, or even KP openings.

For example:

1.Nf3 c5, now 2.c4 is an English, 2.e4 is a Sicilian, and 2.g3 will lead to some "non-Reti" position, like a KIA or Reversed Grunfeld, depending on the d-pawn.

1.Nf3 Nf6 will often lead to an English or QP opening.

1.Nf3 g6 will typically lead to a Modern Defense or some transposition to a Symmetrical English if ...c5 is played.

The Reti is not an opening for players below expert level.

I do okay with the Reti. When I look at GM games and they play it, I'm always surprised to see that I have a fairly positive win rate with it 💀

The very old Batsford book by the late Soviet GM and trainer Viacheslav Osnos gave me a good grounding thirty years ago. I'd suggest pick up a copy of that as a supplement to something up-to-date. If you have a good flexible feel for position and that's your strength whilst other areas of weakness are holding your grade down, go for it. Otherwise, I'd advise much like @ThrillerFan . When I played classically as Black, I found the Reti well annoying to meet.