How much of a weight difference do you think there is between a 16" 205 width tire to a 17" 215 tire?
Is it minimal or pretty substantial? Will it effect the overall performance of my car?
There is probably minimal difference in the tire weight. The bigger tire is wider, but has a shorter sidwall.
The big difference will be in the wheel. 17's are heavier, and the weight is further out from the center increases the rotational inertia making it harder to accelerate and slow down.
I found when i put 17s on that it was noticibly slower to launch. (also due to my tire size 215/45R17, the overall diameter of my tire increased by 4% changing my gearing slightly, making for slower accel, but higher top speed).
To compensate for the heavier wheel, maybe i should suggest a 215/40R17 tire.