Hello Waterwingz,
First of all thank you very much for your interest and kind reply.
I provide a few additional info about the camera behavior.
When you connect the camera to a PC and switch the camera on it first enters into Presentation mode. Then it detects connection to the PC and after a couple of seconds it switches off the screen passing in slave mode. With OTG, this doesn't happen and the screen remains on with all Presentation mode functionalities available.
So I believe that the problem is with the camera SW. I questioned Canon who told me that G15 doesn't support OTG connection.
Should I try a non-OTG cable? But in such case I think the Smartphone wouldn't pass in host mode...
The only way is to force the camera recognizing the OTG connection, but I don't know how.
About CHDK, I'm not using it , I have just discovered it and not yet fully understood its use and functionalities. May be it already fill the gap and solve my issue?
The applications in the Smartphone can read memory sticks and also memory of Panasonic FX38 camera. Unfortunately I don't have older Canon cameras to check.
Many thanks for your help