### What this PR does / why we need it?
This PR updates the release notes for `v0.15.0rc1` to:
- Mark the `310P MoE and W8A8 Support` feature as experimental.
- Add a note for `Kimi-K2.5 Model Support` clarifying that it has known
issues in vLLM 0.15.0 and requires manual patching to work correctly.
### Does this PR introduce _any_ user-facing change?
No, this is a documentation-only update.
### How was this patch tested?
N/A (documentation change).
- vLLM version: v0.16.0
- vLLM main:
15d76f74e2
Signed-off-by: wangxiyuan <wangxiyuan1007@gmail.com>