Double heading driving is a major effort to add extra power to a train. This power is then needed to overcome the adhesive power t heavy trainsTS2015 does not always support driving using double headers. In comparison with MSTS driving with double headers was always possible regardless the engine or differences in traction. The differences between type of traction causes sometimes a problem when a steam locomotive leads.
Some combinations are possible to do but difficult to handle. An example is a leading German class 03 and a German class E18. The problem is mainly the reverser. Because when the regulator is operated the throttle is operated as well. The steam reverser is in use to adjust the cut-off, but a electric or diesel does not have a cut-off system, it just switch forwards or backwards. There is no in-between scaling. This issue causes the main problem in the firt place. However MSTS was able to deal with this differences, TS2015 does not, unless the creators of steam engines has program the engines to make it possible to drive double headed.
Double headers are possible at:
Just Trains 4MT
Just Trains 6MT
Port Road Black 5 in AI traffic only