Could Germany build slow, heavily protected siege battleships?

The video proposes that Germany might accept roughly 18-knot battleships instead of insisting on 21 knots. The saved weight could support thicker armour, more guns, greater subdivision, and the staying power needed for a coastal battle. These ships would have to survive the island's batteries and local light forces before facing the Royal Navy. Their mission would be to sell themselves dearly in a constrained North Sea siege, while Britain retained the industrial capacity to build more hulls. The concept therefore values endurance and destructive power above speed or global deployability.