Your Scott bike is a pretty good commuter.
In my experience of 700c and 26" commuter wheels, the diameter plays a very minor role in efficiency. People do time trials and triathlons on 26" road wheels. Your 26" MTB-slicks are quite efficient with a bigger air gap for better reliability on potholes. You are not comparing an ultra-light road-race setup to a heavy duty off-road wheelset, just standard commuter wheels.
My new commuter wheel has a DT XR 4.2D; a disc brake xc rim at 400g. Mavic open pro is 430g so you wont save weight going to 700c.
Tyres play a big role. Make sure you are using a quality tyre of suitable width for your road surface , weight/load. The lighter and more agile you are the narrower you can go although I am having fun with Schwalbe Big Apples which float over cobbles and roadworks.