The quesiton is, can the Vandread be called a Realistic Mecha or a Super Mecha? (Surely it's called the Super Vandread for a reason) 'Cause the Super Mecha Die Buster seems hard to top.
On topic, my summary/opinion on Episode 15:
It definitely feels like a Gundam show now. Action and tense moments abound in this episode. The Gundams get beat up pretty badly due to an excellent strategy from all three nations taking part in this. Terrorists are used as bait to get a pair of Gundams into a trap, then the real forces unleash a barrage while sending some of their mobile suits.
Having predicted such a turn of events, Virtue and Exia come out of their camouflage, and Virtue uses its GN Paricle cannon to create an area for the Gundams to retreat while taking cover from the barrage. However, the enemy forces get to Virtue and Exia sooner than expected and the other two Gundams are not able to go anywhere. The battle continues for 15 hours. (Which is a ridiculously long run-time, even for a Gundam with how much energy they burn.)
The pilots are getting tired by this point. The enemy barrage stops, the Gundams split up, and the 'elite' fighters come out. The Gundams are seemingly captured in quick order, with Exia having to go against a Mobile Armor. Suddenly, a new Gundam appears with red GN Particles and manages to free Exia.
Definitely one of the best episodes, though I think the next episode preview spoils a few too many things. I actually don't have any other complaints. They even managed to show my current two favorite characters in the beginning of this episode for a short bit, Saji and Louise. (Please don't think less of me for writing that.)