I was really going for a Normal 40k list as I have nvr played escalation. For AT i was was thinking I could tweak the list and add two Vindicator preds or a Laz pred. As far as AV15 the only things that I can think of that I could truly count on hurting it are:
Vin Preds, chain fist Tremies, assault Centurions and Sternguard in a drop pod. Of these the only one that I can count on making it across the field to hurt it are the sternguard. All exp. units
The main problem I come across is I can make a strong list to kill AV (tank spam or forts ) or a Strong list to kill horde (Orks or Nid/Chaos MC spam). I can't seem to come up with a good one to kill both.
But that could just be me being short sighted that why asking here.