On the hodgdon link Hildago provices thay give you a charge of 25.0-27.0gns of Varget for the 60 gn vmax. I have found my best accuracy being somewhere between 26-27gns. I set my COL at 2.26. I've shot this load in several guns and it is a very accurate and well known load at my varmint calling club. Most guys found 26.4 to work best. I use either win or rem std small rifle primers. I only have one ar that likes the 27gn full house load and that is a bushmaster with a 5.56 chamber which is a little bigger than a std 223 chamber; and thus, it handles higher loads better that a tight chambered ar. I would bet that your R15 is a 5.56chamber. If it is, it will be stamped 5.56 on the barrel. If it is stamped 223 Rem, it will have a tighter chamber. Beware of the differences.
Don't get stuck on one bullet. I wanted to use 100 gn ballistic tips last year in my 25-06 for antelope. I couldn't get my gun to shoot them straight. I went to the 117gn sierra game kings, and it is a real goog shooter. If your barrel twist is 1n9 or tighter, you may also want to try the 65gn sierra game kings. I know of an ar that wouldn't shoot the 60 gn vmax straght, but shoots them real well, and It is a great dog load.
Good Luck