Mobile controlled transparency shader

I'm pretty new to any shader or programming. So my issue is, i had done following shader:

  Shader "Mobile/Background A" {
  Properties {
  _MainTex ("Base (RGB)", 2D) = "white" {}
  _Alpha("_Alpha", Float) = 1
  }
 
  SubShader {
  Tags {"Queue" = "Background" }
         Material { }
         Lighting Off
         Zwrite off
  
  CGPROGRAM
  #pragma surface surf Lambert alpha
 
  sampler2D _MainTex;
  fixed _Alpha;
 
  struct Input {
  fixed2 uv_MainTex;
  };
 
  void surf (Input IN, inout SurfaceOutput o) {
  fixed4 c = tex2D(_MainTex, IN.uv_MainTex);
  o.Albedo = c;
  o.Alpha = _Alpha;
  }
  ENDCG
  }
 
  Fallback "Diffuse"
  }

It is not fast enough. Is there any obvious mistakes that i made?

WBR.