A colt- especially that age- should NOT be on sweetfeed, much less as much as or more than the average horse. Sweet feed contains large amounts of sugar, which can be very harsh on a horse's digestive system. They are generally made up of mostly molasses, corn, starches, and other sugars. All of these things are extremely hard to digest, can make risks of founder/colic higher, and ofcourse- can make a horse hot!
Why is he not still suckling? At this point he needs to be taking atleast half of his nutrition in by milk, not feed. I'd be really concerned right now, especially if he's overweight. Calling a vet out and getting him on a higher-nutrience feed, as well as getting his feet trimmed if you think they're too long would be the first steps. Founder is a very serious thing that can ruin his life or even potentially end it. You can't be too careful