Set the Culture and UICulture attributes of the @ Page directive
.aspx Page
<![CDATA[<%@ Page UICulture="hi" Culture="hi-IN" %>
C#.page
decimal Val1 = 155000;
TextBox textBox1 = new TextBox();
textBox1.Text = string.Format("{0:C2}", Val1);
Updated:
textBox1.Text = string.Format("{0:N2}", Val1);