Since we have the thread about the fastest army; what about the slowest?
I have three guesses: 1) Anything with a lot of elements: Ming Chinese, dismounting Knight armies, dismounting armies in general. 2) Anything with elaborate dresses, extra points if they also do not wear a uniform. Thracians are bad if done right. So is everything with heraldry. 3) Anything you really want to paint well.
My slowest army have probabyl been the Celts, but that is due to the large number that I am doing for my morphing project. For a single, normal sized army, it was the Ancient Spanish, because I wanted to paint them well.
For me it is the Mongol Conquest, Essex figures I bought in 1990 from Gamers in Exile, London before it got pulled down to make room for the Kings Cross Eurostar terminal.....that's how long ago. So 27 years and still not a single figure painted! One day.....
However, to answer the question more appropriately then one of the IV/13 Mediaeval German options must be in the mix. The 6Kn options mean lots of knights and lots of heraldry to slow tings down plus lots or "or" options to ramp up numbers.