Slower speeds?
Nope, not a chance in Hell, because:
Slower speeds means wetter washing.
Wetter washing takes longer to dry in our climate.
Longer drying times are inconvenient to modern households.
Wetter washing would cost a fortune to dry in a tumble dryer, especially with our electricity prices.
And I've witnessed lower speeds being rather violent in their movements. Whereas faster spins can be more stable. However, much depends upon the design of the machines. Some are much better than others.