Maybe a 15 is plenty for your style of shooting, but the rifle in question is equipped with a 9X. Come shoot steel dogs with us with a 9X and lets see if you like it.
I don't hold for elevation, I dial, so the reticle only being accurate at max power is irrelevant to me. The fact that your 2nd focal plane scope doesn't work at various magnifications doesn't invalidate the idea of buying a higher power scope and dialing it back to cope with mirage. For your style of shooting a FFP scope would be better suited than the NF you are using. The prices of those scopes are coming down and the number of choices is increasing. You might consider looking into trading off the NF. That's a pretty hot scope and is in big demand. I see them going used for nearly the cost of new.
To the OP, I still think that 3X9 is unsuitable for long range/small targets.