Maybe tweaking the settings for auto-complete will help.
Indeed, setting INPUTSEARCHDELAY to 2000 did help here a bit.
But yes, it is dramatical slow and bad responding. With the Selection Cycling on, most times the focus of the commandline is lost so it does not react to an Enter, have to press it twice, if not the InputSearch found some completely other command yet. In Civil3D I noticed also that if I click on a Civil3D object, the activation of a contextual Ribbon also sometimes result in a lost focus of the drawing area.