The 'override input device' had to be set to 'Steering Wheel' (when using a wheel), to remove the damping that was being applied to suit gamepads.
With gamepads, they have small controls with a small range of movement, they maybe analogue, but the small range of movement makes them very sensitive. It so easy to oversteer with your thumb on a little joystick, and you could end up zig-zagging along a straight piece of track.
So to help with steering a form of damping was introduced, (a far as I am aware), to make steering with a little joystick easier, damping out the little control inputs, smoothing everything out.
If you apply that same damping to a steering wheel, it feels unresponsive, hard to turn into corners, like it was understeering. This is what the 'override input device' > 'Steering Wheel' setting was about, it was switching off that damping used for gamepads. So raw wheel movement data was being sent to the game.
I don't know whether you read the first post in my sticky about wheel settings, but as far as I know the info is accurate. So even though you might lose that 1:1 visual setting with the in-game steering wheel, you might be able to tweak your control problem out of the wheel with the saturation and/or linearity settings.
http://www.racedepartment.com/threads/f1-2015-steering-wheel-controller-settings-list.105081/
Sorry ignore that last paragraph, it slipped my mind that you don't have a supported wheel, so you don't have access to the saturation and linearity settings ...... doh!
I really don't know what you can do, apart from hoping that your wheel will be supported in a future patch
Cheers