We are also running into this issue. We're on Unity 2020.3.33 LTS. I'm also only seeing 1.15.18. If I enable preview packages I see many 2.0.0 previews, but I cannot find any reference to v1.17.0. The documentation (https://docs.unity3d.com/Packages/com.unity.collab-proxy@1.15/manual/index.html) also does not mention 1.17. Where can we find this package?