Subnet mask 16 bit 24 bit.

I had a user (Windows Admin) who made a request to have our subnet mask on our NAT end from 16 bit to a 24 bit mask.
His chief concern was the windows machines performance, which he said was being impacted by all the Broadcast traffic.
We are a large network with Mulitple Gig Backbones and the LAN traffic has a lot of “head room”

My question is this a valid concern/issue?