Greater Chest Capacity for Mules and Donkeys

As they are now mules and donkeys are much worse than horses.

They are significantly slower and can jump much less high than horses, as well as not being able to wear horse armor. I don't even remember the last time I saw someone use a donkey/mule. 

That is why I think a donkey/mules chest capacity should be raised to as much as a double chest (54 slots). This may sound ridiculous, but I think the difference between their speed and jump height compared to horses is so great that it is justified. It would add a genuine use for mules or donkeys as a way to carry large amounts of materials of long distances, which isn't possible with the meager 15 slots currently available. However, if 54 slots is too excessive, the same amount as one chest (27 slots) would also be a significant improvement.

With this improvement I think players would have to put more thought into which animal they use (horses or mules/donkeys) depending on what they need it for.