poke around the racingfuelsystems website or just google holley idle feed restrictions.
assuming you have yr prim thorttle plate in the right spot, leaning out the 1500 rpm range probably only will involve a smaller idle feed restrictor (or sometimes called idle jet, or IFR). do the metering blocks have replaceable IFR's ? they will be up high most likely, in the upper outside corners.

you probably want to go down in size about .002, so say .035 to .033
you can also hone in on the afr's some by going larger on your idle bleed which should be adjustable on that carb.

this is just a page i pulled from a websearch, it shows the IFR location in most holley blocks.
http://tmpcarbs.blogspot.com/p/blog-page.html