Mobile: Diffuse Cutout shader with NormalMap. Very bad performance.

Good afternoon. I tried to use such a simple cutout+normalmap shader for my lianas: Shader "MyShaders/Light_CutOut_Color" { Properties {

       _Color ("Main Color", Color) = (1,1,1,1)
       _MainTex ("Texture", 2D) = "white" {}
       _BumpMap ("Bumpmap", 2D) = "bump" {}
 
       _Cutoff ("Alpha cutoff", Range(0,1)) = 0.5
       
     }
     SubShader {
      Tags {"Queue"="AlphaTest" "IgnoreProjector"="True" "RenderType"="TransparentCutout"}
      Lighting On
 
     LOD 20
       CGPROGRAM
       #pragma surface surf Lambert alphatest:_Cutoff 
       
       struct Input 
       {
           fixed2 uv_MainTex;
           fixed2 uv_BumpMap;
       };
       
       sampler2D _MainTex;
       sampler2D _BumpMap;
       fixed4 _Color;
      
       void surf (Input IN, inout SurfaceOutput o) 
       {
         fixed4 c = tex2D(_MainTex, IN.uv_MainTex) * _Color;    
         o.Normal = UnpackNormal (tex2D (_BumpMap, IN.uv_BumpMap));
         o.Albedo = c.rgb;
         o.Alpha = c.a;
       }
       ENDCG
     } 
    Fallback "Transparent/Cutout/VertexLit"
   }

All textures are 512x512, poly count ~ 1000. So when I run near the model, FPS falls from 50 to 25.

Can you help, is it possible to use cutout + normalsMap in more optimised way? Thank you very much!