Excess protein in the diet can have serious side effects including bladder and kidney stones, IR and Cushings disease, so it is important to make sure your horse is not getting too much protein for the level of growth or work he is doing.
When I am looking for a pelleted or extruded feed I like to see beet pulp, flax, soybean hull and rice bran listed as the main ingredients as these are all good sources of fat and energy for horses and will usually provide a good balance of fat and protein as well as being easier for the horse to digest. Grain based products are digested differently from forage or forage like sources and when fed in large amounts can contribute to severe hind gut issues, as well as aforementioned issues caused by feeding too much protein and NSCs.
If switching feeds is not possible, I personally would be inclined to have my horses taken completely off the pelleted feed and instead fed more hay.
They say money doesn't buy happiness -- well happiness doesn't buy horses!