I have hunted 51 ten times during the archery seasons of the past 20 years and while I haven't hunted 15, I've hunted a neighboring unit and have a good friend who is a guide and lives in 15 so I see his pictures and have scouted out of his place several times.
15 has much better Genetics and larger horns. 51 has very tasty elk but mostly skinny horned CO type bulls. There are a few large ones there, but not many. Skinny 5 X 5's pretty much all over the whole unit. Its a fun hunt but I certainly wouldn't spend "trophy $" on it.
First weekend in October they should still be pretty vocal. Just stay away from the crowded areas like Trout Lakes and the country between there and the HWY and you should do well. The East side of the unit gets much less pressure but still has elk. However, the whole unit gets a considerable amount of year round poaching so the elk are very road shy. Get off the road a half mile anyplace and you will do well. Lots of bears as well. Used to be some whopper mule deer but haven't hardly seen any the past several times we have been there.
