It would be an interesting game since the map would be large enough for both nations to fully use their abilties. And its probably true that Caelum is one of the best opponents for Pangaea (much better than a head-2-head nation such as Ulm or Pythium). Some of my favorite tactics for Pandaea (and I do have others) just doesnt work well on small map games.
But yes 1500 was shooting for the extreme. In fact its the maximum number of provinces that the game presently allows. None of my 1500 games have ended yet.
Its also a very different game to generate a map with mountains at 50 which creates almost a maze of chokepoints.
And to give each province a chance of a completely random squad. It really forces a change in strategy to find a province that you HAVE to go around. Such as finding that it has a Sphinx there with Tree Lord bodyguards and Manticore troops. While the next one has a slinger leader with monolith bodyguards and turkeys as troops.