Media Encoder 15.2 (Build 30) Maxxing Out Bitrate?

Hi there, kind of a weird issue I've been having lately. I've had some deliverables for clients lately that call for specific bitrates in the specs. But encoding certain types of videos, specifically graphics-heavy pieces with lots of block colors, despite selecting h.264 with CBR of 15mbps or something, when reading the file in VLC or Quicktime, it shows only around 2mbps. It's almost like it's compressing it to a lower bitrate than I set it at, because a higher bitrate isn't necessary for the video.

Any ideas? In this example, I'm encoding from a ProRes 422 HQ clip, to H.264 MP4, using CUDA, on an ASUS 3070 TUF.