What makes you think it would slow it down?
Whatever size of wheel you fit, the total diameter of the wheel and tyre together stays the same. If you fit bigger wheels, you fit correspondingly shallower tyres...
Any you don't have to lower the suspension just because you've fitted bigger wheels - its a completely separate thing.
You can lower it with the same wheels if you want....
People lower the suspension to simply make the car look better. When they do, they usually fit stiffer springs, because you need more resistance if you haven't got as much suspension travel - but that does lead to a harder ride...
Sport and S-Line models got lower suspension as standard fit....