Whew - you have a mess starting and it is apt to get much worse with that ratio. If I count right you have 5 cockerels and 3 pullets all at 15 weeks of age. That is almost a perfect recipe for a wreck.
Yes, I think he is getting bullied, and more than likely not enough to eat. With that many cockerels you are going to have cock fighting, especially if you have a smaller coop/run.
I think the pullets are going to be next, with multiple matings, feather pulling, and biting by the other roosters. That ratio of roosters can literally wear pullets to death, and rather a horrible one at that.
You really need a way to separate birds, I am a wondering what kind of set up do you have as in measured space, and type of coop. Not sure where you are, but going into winter with that ratio of males to females is not good.
I would cull all the roosters ASAP. If you cannot cull them fore personal use, re-home them and do not ask questions. Do not try and sell the roosters, give them away. You have too many to wait.
At the very least, you need some dog crates to separate birds immediately ready to go, even if you think they are all getting along. How cockerels act today, is no indicator how they will act tomorrow, and when it goes south, it seems to do it out of the blue.
Mrs K