I'd much rather have a couple high-quality pollsters showing D+10 than a pollster with a dubious track record and methodology showing D+17, but you've gotta take what you can.
And, granted that I have never been alive for a D+17 let alone D+15 electorate, but individual polling and each party's strategic investments (hinting at their private polls) do not suggest such an environment. I seriously doubt Democrats would be falling behind in the Senate if it electorate was that anti-Republican, nor do I think someone like Hurd or Valadao would look like favorites for reelection.
I dunno, the individual polls definitely do not support a D+15 electorate, but some of the investments do. SC-01, for example.
