I would suggest trying an improved cylinder choke. I'm not familiar with Beretta's, but, if you were shooting a Remington I would suggest having someone lengthen the forcing cone.
At 15 yards the 1B should do better than that in my experience (which has been out of 870's)
The physical difference between the size and number of pellets in 1B and OOB means they arrange in the flight control wad differently, so I'd get an IC choke to try with the OOB.