InDesign data merge printing VERY slowly

I have a 2-page letter in InDesign with four graphics. I've made resolution on the graphics as low as possible to still look good when printing. My data source is aout 3,200 records. I'm merging/printing 250 at a time because of how slow the print process is. It's taking about 90 minutes per 250 letters.

Any help will be much appreciated!