Can you advise what speeds you see?
We have broadened this to more machines and it is 5 seconds or so on a LAN in same office and extending to 18 seconds to get to hosted machine.
conn.UseADLogon = true;
conn.EndpointIdentityType = EndpointIdentityT.UpnIdentity;
conn.PrincipalName = "firstname.lastname@example.org";
the connect method has been tried passing either true or false with same results
s = c.Connect(conn, true);