Yeah, they are disproportionate to the rest of the body. Which isn't bad, you just need some more anatomy study, that's a common mistake. I saw a critique someone left on a work of yours and they suggested a couple of pretty nice books, I'd start from there if I were you.
1. Her ass is NOT too big. That is NOT the problem here. The main problem here is over all proportions. A. Her ass doesn't fit her hips. Try to focus on the shape of the pelvis. B. Her arms are too short. Elbow should be even with the thinnest part of her waist I think.(Or is her whole upper torso too short?) C. Neck is a tad too long and she can't turn her head around that much. D. Hips and waist are waaay too narrow. Make them wider and show the muscle and fat underneath to give it a fleshier look. E. We see no sign of adipose fat, skeletal structure and muscle mass underneath. F. Cheeks themselves have the wrong shape. They seem square to me. G. The right cheek that's further away looks out of focus. It's further away so it should be smaller.(forshortening) Like here ---> [link] - [link]
2. There's a difference between "her ass is too big vs her ass is out of proportion" Here's an example of asses that are actually bigger than what's in this picture but the body is proportioned with the ass much better. ---> [link] - [link] As you can see the butts are huge. But the rest of the body connects to the huge asses correctly.
3. Like you, I love big asses. Especially the ripe juicy plump asses of many Black women. But what you have to understand is that in order to draw the ass correctly we've got to understand anatomy/physiology. The waist, hips, spine, thighs and legs need to fit into and around the butt cheek correctly. Check here ---> [link] - [link] - [link] - [link]
4. Now to those who say it's too big. Wrong. Everything else is off. And yes black chicks Not all! can and do have asses that are quite large. So the ones saying silly things IMO are a bit short sighted. Yes I'm black and I do consider myself somewhat decently versed in human anatomy. And I always try to learn knew things about how the human body operates.
5. Black women do tend to have bigger butts, smaller waists, denser bones, thinner longer limbs, smoother skin slightly less body fat(the healthy ones) and also there's some research I've found that many black people have an anterior pelvic tilt. Pelvis tilts slightly more forward making our butts stick out more and giving a slightly more curve to the spine. This supposedly gives black athletes an advantage in things like running, sprinting or any other sport that requires much leg work. [link]
6. Finally I would like to say that IMO Brandon you're a pretty good artist. If YOU are comfortable with your art style. Than don't change anything. But if YOU want to improve and make sexy, attractive black women that look more realistic. Then you definitely should check out the links and get deep into female anatomy. Especially black womens physical anatomy. ---> [link] - (i didn't fully read this but it might help) ---> [link] - [link] - [link]
Definitely give you a 7/10. Could be much better but not that bad. Just needs some tweaking. But again that's up to you whether you want to improve or mot.