What else are you currently reading in Latin?
I'm working on chapter 47 (half-way through) and I also think Roma Aeterna is quite hard. For some reason I find it not too difficult to read although the chapters are fairly long and at times I struggle with the odd sentence here and there, but in reality the strange Greek names and the sheer amount of new vocabulary are slowing me down more than anything else. That's why I try to read every single chapter twice, understand at least 95% and try to do the
pensa before moving on. Right now my primary goal is just to get through the whole book and then read it again to really absorb as much new vocabulary as possible.
Familia Romana was great. I read it twice and revised the last 10 or so chapters before really jumping to Roma Aeterna. Reading several complete beginner and intermediate level books has helped quite a bit, and I also went through the first chapters of Roma Aeterna two or three times before moving on. Trying to read Catullus after Familia Romana was also definitely worth it!
The general order in which I started to read books written in Latin was the following (with great inspiration drawn from the suggestions of Daniel Pettersson): Colloquia Personarum, Pugio Bruti, Ritchie's Fabulae Faciles, Harrius Potter et Philosophi Lapis, Ad Alpes, Winnie Ille Pu, Fabulae Ab Urbe Condita, De Bello Gallico. There were probably others that I just don't remember. Soon I'll finish reading De Bello Gallico and move on to something a little less bellicose.
Anyways, I think Roma Aeterna requires some true tenacity and perseverance. If Familia Romana takes you to B1 level, Roma Aeterna is definitely closer to C1. There is a gap that can only be overcome by reading quite a lot of something else in between.