my E320 just lateley cruise problem

It could be many things. Best to have the vehicle properly inspected for these codes. The code P0715 is the turbine input speed sensor, which is a straight forward repair, just remove the old sensor and install the new FACTORY sensor. Then clear the codes and see if the P0726 comes back. because the turbine input speed sensor is a primary sensor that can effect many functions of the transmission. The P0726 is an engine speed input malfunction, which could be caused by the turbine speed sensor. So I would do the above repair, clear the codes and then drive the car to see if the other code comes back, it may not.