Our D3D Device is created in windowed mode. After resing the window, we must dispose the device to avoid crashing or image stretching, and then to recreate it. Recreating the device is quite slow and shows as disturbing flicker when resizing it with mouse.

Is there any option to create the Device faster, or resizing the device, resulting faster and non-flickering window resize?

Have you tried using IDirect3DDevice9::Reset() with the new presentation parameters instead of tearing down and rebuilding the device? It should be a lot faster, and it's something you would need to do anyway in response to D3DERR_DEVICELOST.