With the engine getting stuck at 15% N1 that suggests that fuel is not being fed to the engine. In the aircraft, double-check that you have the ENG1 fuel pump switched on and throttle 1 in the FUEL ON position.
However, with it just being one engine that is not starting, that could also point towards a controller conflict. To rule this out, I would recommend temporarily unplugging any external hardware that you use for flight simulator (joystick, throttle quadrant, etc.) and then start a new flight in the 146. If all the engines start correctly with the external hardware unplugged, then we can narrow down the cause to a control assignment linked to a control on the external hardware.
Mark - Just Flight