The wheel set with tyres must weigh around 5kg, all that alloy and rubber?
I don't know what the wheels and tyres weigh but in under the physical laws governing "Moments of Inertia" extra weight at the outer edge of the wheel will be an issue.
To quote from Wikipedia:
Figure skaters who begin a spin with arms outstretched provide a striking example. By pulling in their arms, they reduce their moment of inertia, causing them to spin faster (by the conservation of angular momentum).
With FatBikes, evidence from the large slots in rim show that this issue is being addressed.
These days low pressure tyres don't have to be heavy though using puncture sealant is recommended as lightweight fat tyres are more likely to pick up thorns etc.
The effects of Moments of Rotation, where their is too much weight at the outer edge of a big wheel, can be large. Don't tell the 29ers, but according to the theory, large wheels even of the same mass as smaller wheels take longer to roll down a given slope. They simply require more energy to accelerate them.
In practice this is very noticeable. My 1983 Cleland where the tyres weigh 3lb each is noticeably slower than my Cleland fitted with lightweight Racing Ralphs.
The main effect though is on quick acceleration. The modern lightweight tyres are much more lively and can noticeably reinvigorate an old bike.
When it comes to Moments of Rotation, Alex Moulton is on the money with his 16" lightweight wheels and suspension. On hard surfaces you can really feel the difference. However, on anything softer than tarmac the wheels sink into the ground and the rolling resistance becomes horrendous. It can feel as if you're towing a car behind you.