No offense to Legairre, and I don't have the 1500, but raising the IRE to 7.5 will most likely make the black level WORSE (as in brighter).
Also, chances are increasing the gamma level will also do the same.
To test the true "black leve" of your projector, turn the brightness ALL THE WAY DOWN on a black screen and see how much light is still on the screen. Is it a bright, dull grey? If so, the only thing you can do is use an ND filter in front of the lens. This will dim the entire image, but black level performance will significantly increase. Then you can increase the gamma to bring back shadow detail.
I did this on my Infocus 5700 and was very happy with the results (especially since it's a very bright projector to begin with).
When you first do this, you will be inclined to think your image is too dark... but live with it for a few days and get used to it first; if you're watching in a totally dark room, chances are you will be satisfied with the amount of light you're still getting and MUCH more satisfied with the picture quality!