They spend 15 minutes/trip + 30 minutes/trip = <<15+30=45>>45 minutes/trip filling the car and driving to the new house.
They had to take 6 trips, so they spend 45 minutes/trip x 6/trip = <<45*6=270>>270 minutes.
They also had to drive back to their previous house 5 times to complete the move: 30 minutes/trip x 5 trips = <<30*5=150>>150 minutes.
In total, they spent 270 minutes + 150 minutes = <<270+150=420>>420 minutes.
Each hour has 60 minutes so they spent 420 minutes ÷ 60 minutes/hour = <<420/60=7>>7 hours in total.
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