Notes:
- I've never tried the 215s in my PRC, but have played a little with 220s - use 230s as my go-to. Unfortunately, 230s (the non OTM Tactical variety) are impossible to come by. I'm on my last ~200 and will be switching to the OTMs when out. I don't think that changing the bullet should be your first step - probably your last...
- I jump my 230s at .039. The Berger hybrids are very tolerant of jump changes, but you might want to try playing with seating depth first. I take my arbor press to the range with a bunch of rounds loaded long, then size down as I go, find a promising depth, finally run the rest through to validate (or not). The only hybrids I've run at > .040 are 155 Full Bores for my new 308, and only because of mag length issues. Every other Berger hybrid I've used (200.20, 205, 220, 230, 245, 105, 109) have performed better at lower depths.
- I think N570 is too slow, especially for the 215s. I haven't played with it in my PRC, but have messed around with similar slower speed powders like RL33 and it did not yield good results. H1000 is a better bet, RL 26 better yet (if you can find it). As
@rustyinbend said, Retumbo can work, but sometimes it turns into unobtainium like RL26 is now (not just now, actually). H1000 tends to be more available across a longer period of time.
- Carbon barrels can get wonky
A couple years ago, a now-friend of mine had a light weight 300 PRC hunting rifle made with a carbon barrel. He couldn't get it to shoot (remotely close to shoot, actually) with factory ammo - like 2-3" groups at 100. I met him because we both used the same smith, and said smith contacted me because of my experience loading for the PRC. Before I could help, my now-friend said he couldn't believe that tuning a load could bring it in that much, and asked the smith to rebarrel with a different manufacturer's barrel. The newly minted barrel/rifle came in and it shot perfectly... badly... again... same result. So, now we went through the exercise of load development, and at least we were able to (with minimal effort) bring the groups down to sub-moa. He subsequently got into reloading, worked more on the load, and is only now happy with the results. Long way of saying he's shooting Berger 205s at .040, ~2930 fps.
Lots of words - TLDR:
- Move to H1000 first. EDIT: was typing when you wrote that you scored some Retumbo - play with that.
- Play with seating depth second
- If you have changed powder, found a good node, and run a full depth test starting at like .015 off and moving up to ~.050, only then think about changing bullets (unless you want to for other reasons). There is no reason the 215s should be a problem.