It will be fairly moderate. On a scale of 1-10, it's probably a 5 or 6. Many schools in the south are out for the summer by then, and families try to squeeze in a trip before the summer onslaught.
We were there a week earier last May, and our longest waits were about 25 minutes for Astro Orbiter and 15-20 for the Great Movie Ride (both non-FastPass attractions.) If you use FastPass liberally and tour wisely, you'll rarely wait more than 15 minutes for any ride.