My take on this. We also struggled a bit with my daughter when she was about 15/16. I tried using a Librivox recording: https://librivox.org (just search for Ben Hur) That worked for several chapters. However, we both decided to drop it and just go onto the next suggested book. All went ok.
We at least ‘tried’ the readings, and were able to appreciate the writing style and learn from it. The other is that, to be honest, throughout all the 8 years of home schooling, we read through some books 100% and some 50% and some less, depending on our life circumstances, her current growth level, etc. In other words, we adjusted to our needs.
Yes, we sometimes need to push through and persevere, but also we need to be able to move forward and adapt. The other home school vets on here, will most definitely have their own spin on that.
So in conclusion, keep going, maybe break it down in smaller chunks, skip chapters, use audio or physical book, have a family member read with them, other kids their age, watch a Ben Hur movie, etc. If not, then try your best and move on to something else and or a substitute.