Increase it’s effect from 10% up to 15%.
Also affects prelates.
One of the biggest issues with HRE infantry is actually being able to engage opposing kiting units, as well as needing mobility for either flanking and/or map presence.
Cavalry will always be superior in this regard, but at least by increasing the effect of Marching drills, it makes MAA faster than most opposing archers, so they have the potential to catch up (currently they are equal speed, so if the archers dont fire, the MAA will never catch them)
It will allow spears increased mobility to reposition vs opposing cavalry.
Gives the landsknecht the higher speed it needs (although this unit needs an all round buff / cost reduction anyway)
And finally it gives the prelates the desperately needed higher speed they need to keep pace with the army (even if their ability needs a fix as well)