A car does not have an arm that picks up heavy objects. The ones that do (crane trucks) need outriggers and jacks to stabilise the machine and stop any motion before they can extend their arm.
Of course it depends on the weight of what you are moving, but it doesn't seem like the 2 wheeled robots in the video can actually move "heavy" weights.
I would not call 15 Kg "heavy". I can carry that myself on a single arm...