Why can't I import my Blockbench java model?

// Made with Blockbench 3.5.2
// Exported for Minecraft version 1.15
// Paste this class into your mod and generate all required imports

public class custom_model extends EntityModel<Entity> {
    private final ModelRenderer Penguin;
    private final ModelRenderer Head;
    private final ModelRenderer Body;
    private final ModelRenderer LeftFlipper;
    private final ModelRenderer RightFlipper;
    private final ModelRenderer RightFoot;
    private final ModelRenderer LeftFoot;

    public custom_model() {
        textureWidth = 64;
        textureHeight = 64;

        Penguin = new ModelRenderer(this);
        Penguin.setRotationPoint(0.0F, 24.0F, 0.0F);
        

        Head = new ModelRenderer(this);
        Head.setRotationPoint(0.0F, -14.0F, 0.0F);
        Penguin.addChild(Head);
        Head.setTextureOffset(12, 41).addBox(0.0F, -2.0F, -3.0F, 2.0F, 1.0F, 1.0F, 0.0F, false);
        Head.setTextureOffset(0, 17).addBox(-2.0F, -6.0F, -2.0F, 6.0F, 6.0F, 5.0F, 0.0F, false);

        Body = new ModelRenderer(this);
        Body.setRotationPoint(0.0F, 14.0F, 0.0F);
        Head.addChild(Body);
        Body.setTextureOffset(0, 0).addBox(-3.0F, -14.0F, -1.0F, 8.0F, 13.0F, 4.0F, 0.0F, false);
        Body.setTextureOffset(24, 0).addBox(-2.0F, -13.0F, -2.0F, 6.0F, 10.0F, 6.0F, 0.0F, false);

        LeftFlipper = new ModelRenderer(this);
        LeftFlipper.setRotationPoint(0.0F, 0.0F, 0.0F);
        Penguin.addChild(LeftFlipper);
        LeftFlipper.setTextureOffset(28, 28).addBox(5.0F, -14.0F, -1.0F, 1.0F, 9.0F, 4.0F, 0.0F, false);
        LeftFlipper.setTextureOffset(6, 41).addBox(5.0F, -5.0F, 1.0F, 1.0F, 2.0F, 2.0F, 0.0F, false);
        LeftFlipper.setTextureOffset(18, 41).addBox(5.0F, -5.0F, 0.0F, 1.0F, 1.0F, 1.0F, 0.0F, false);

        RightFlipper = new ModelRenderer(this);
        RightFlipper.setRotationPoint(0.0F, 0.0F, 0.0F);
        Penguin.addChild(RightFlipper);
        RightFlipper.setTextureOffset(18, 28).addBox(-4.0F, -14.0F, -1.0F, 1.0F, 9.0F, 4.0F, 0.0F, false);
        RightFlipper.setTextureOffset(0, 41).addBox(-4.0F, -5.0F, 1.0F, 1.0F, 2.0F, 2.0F, 0.0F, false);
        RightFlipper.setTextureOffset(12, 43).addBox(-4.0F, -5.0F, 0.0F, 1.0F, 1.0F, 1.0F, 0.0F, false);

        RightFoot = new ModelRenderer(this);
        RightFoot.setRotationPoint(0.0F, 0.0F, 0.0F);
        Penguin.addChild(RightFoot);
        RightFoot.setTextureOffset(22, 17).addBox(-3.0F, -1.0F, -3.0F, 3.0F, 1.0F, 6.0F, 0.0F, false);

        LeftFoot = new ModelRenderer(this);
        LeftFoot.setRotationPoint(0.0F, 0.0F, 0.0F);
        Penguin.addChild(LeftFoot);
        LeftFoot.setTextureOffset(0, 28).addBox(2.0F, -1.0F, -3.0F, 3.0F, 1.0F, 6.0F, 0.0F, false);
    }

    @Override
    public void setRotationAngles(Entity entity, float limbSwing, float limbSwingAmount, float ageInTicks, float netHeadYaw, float headPitch){
        //previously the render function, render code was moved to a method below
    }

    @Override
    public void render(MatrixStack matrixStack, IVertexBuilder buffer, int packedLight, int packedOverlay, float red, float green, float blue, float alpha){
        Penguin.render(matrixStack, buffer, packedLight, packedOverlay);
    }

    public void setRotationAngle(ModelRenderer modelRenderer, float x, float y, float z) {
        modelRenderer.rotateAngleX = x;
        modelRenderer.rotateAngleY = y;
        modelRenderer.rotateAngleZ = z;
    }
}

That is the code for my Blockbench model.

I've got it! Try using 2020.3 Snapshot!