LTSpice's ltline (lossy transmission line) symbol slowing down the simulation process. What can I do?
Simulating a transmission line is hard! 

The Spice model used will be a very long array of RLC lumped elements to simulated the basic model of a transmission line. With so many elements to simulate it will take a long time. Removing the transmission line will in turn remove all the many elements and so it will speed up.