Stop putting your interfaces all inside a folder called "Interfaces"! If I'm looking for the interface for CheckoutService, I don't want to browse through every interface in the application to find it.

I also shouldn't have to import a namespace solely for an interface. Ideally, the interface will be in another project, but under the same namespace as its implementation, in most cases.

Do you see Microsoft putting their interfaces in a folder called "Interfaces"? There's probably a reason they don't.