OK, so after hours of feverish working, I managed to figure out a 1500pts Last Wall army list

It got a bit frustrating there, but in 1500 points I got a Battalion and a Patrol, which isn't the dual battalions I was hoping for but whatever.

Anyway, my list:
Battalion - Imperial Fists
- Celestial Lions Captain - Storm Bolter/Chainsword
- Imperial Fists Terminator Captain - Shield/Hammer
- 2x Celestial Lions Tactical Squad - Multi-Melta/Combi-Melta/Chainsword
- Crimson Fist Tactical Squad - Missile Launcher
- Imperial Fists Terminator Squad - Assault Cannon/Storm Bolters/Power Fists/Power Sword

Patrol - Black Templars
- Black Templars Captain - Combi-Flamer/Power Sword/Jump Pack
- Black Templars Chaplain - Combi-Flamer/Jump Pack
- 2x Black Templars Crusader Squad - Combi-Flamer/Flamer/Chainsword
- 2x Black Templar Sword Brethren (Company Veteran) Squads - Bolter/Chainsword
- 2x Black Templar Assault Squads - Flamers/Jump Packs

The total is a mere 1476 points. I could add Heavy Bolters to the Crusader Squads, but I dunno.