Sorry it took me so long to respond. I just picked up a 308 15" barrel last fall and am playing with some loads now for deer. I have settled on a Sierra Game King 150gr spitzer. I am loading 44gr of IMR 4064 and playing with the seating depth now. It seems to like a little jump because i am out to 20/1000. I believe from the manual i can go as high as 48gr max, but may just stick with the current if i can keep the groups within a couple inches.
by the way, Nosler has loads for the 15" 308 in bullets of 125gr, 150/155gr and 165gr.