Just to clarify, the image you're pulling into Photoshop is less than 1500x1100? Hmm. You're probably stuck with that -- I think Projection Master is 1:1 by nature, though maybe v2.5 reworks this with Zapplink in mind. Maybe.
That said, try playing with the AA:half button -- it might double your effective resolution. Also, hiding all your palletes will give you a little more real estate onscreen. You can save custom UIs to automate the toggling back and forth if that ends up helping.
Please report back if these suggestions are useful or not -- I suspect I'm about to run into the same issue myself!