How to implement same code for 15 linkbutton click events

An Event is simply a delegate pointing to a Method that handles it (there might be a bit more to it, but this part is important). This makes it possible to have multiple Events point (or listen) to the same Method.
Take for instance the following code in VB:

AddHandler LinkLabel1.Click, AddressOf LinkLabel_Click
AddHandler LinkLabel2.Click, AddressOf LinkLabel_Click
AddHandler LinkLabel3.Click, AddressOf LinkLabel_Click

Private Sub LinkLabel_Click(ByVal sender As Object, ByVal e As EventArgs)
   ' Your code here, get the LinkLabel that was clicked by casting the sender.
End Sub

This is similiar to the following code in C#

LinkLabel1.Click += LinkLabel_Click;
LinkLabel2.Click += LinkLabel_Click;
LinkLabel3.Click += LinkLabel_Click;

private void LinkLabel_Click(Object sender, EventArgs e){
   // Your code here, get the LinkLabel that was clicked by casting the sender.
}

Alternatively, in VB, you could use the Handles keyword like follows:

Private Sub LinkLabel_Click(ByVal sender As Object, ByVal e As EventArgs) Handles LinkLabel1.Click, LinkLabel2.Click, LinkLabel3.Click
   ' Your code here, get the LinkLabel that was clicked by casting the sender.
End Sub

I have never worked with ASP.NET, but I am pretty sure this works the same way :)