Jack. RL-15 looks quite a bit like IMR-4895. If you were to put two piles of powder next to each other, one being RL-15 and the othe IMR-4895, I'd be hard pressed to tell them apart. They would, of course, meter through a measure about the same.
IMR-4759 is a short, fat, tubular power that is good for cast lead loads. I have two powder measures, an older Pacific, and two RCBS Uniflows. 4759 does not meter well for me in those, sometimes hanging up and sticking like the 4831's and similar types. I use it mostly in a 45-70.
Just as an aside, Winchester's W-748, according to them, was developed especially for the .308 Win. I just loaded some up to try. My pet loads use W-760, and while velocity is not the highest, they are good accurate hunting loads that I use for deer and elk in the .308.
I haven't used RL-15 in the .308. I'll have to look into that.