Problem with render texture

hi guys,
I try to implement a mini-map system in my game. I have map 2048x2048 and I use render texture to show mini-map on my UI. To show all mini-map I need to set size 1200 on my camera and then I have a huge drop on fps.
I don't know how I can improve the system. any ideas?

code to create texture
_miniMapRenderTexture = new RenderTexture((int) _screenWidth/2, (int) _screenHeight/2, 24)
{
filterMode = FilterMode.Point,
wrapMode = TextureWrapMode.Repeat,
useDynamicScale = true,
memorylessMode = RenderTextureMemoryless.Color
};

I attached camera setting

everything works well if the camera size is smaller but I think it's obvious

duplicate topic from the general channel
https://forum.unity.com/threads/problem-with-render-texture.779633/