Just played my second game using my Basilean Horde which is 17 models strong (200 points).
I did not notice it so much in my first game, but I think it is more models than Vanguard can handle.
In my first game with the Horde I was against a 10 model strong Nightstalker warband. We joked and talked alot and after 3 turns we stopped because it got too late, and decided to have a rematch the next week.
In our rematch we decided to chat less and managed to get through five turns quite quickly in about 2 hours, but my opponent would quickly run out of activations and my turns felt like they just took too long.
When I was using Ogres and had a tiny army, but I was up against about 13 models Vanguard did not feel like it dragged this much.
In my opinion (so far) 17 models is just too big for Vanguard, but I would love to hear from others about their experiences.