Update version numbers for TensorFlow 2.15.0-rc1
Before merging this PR, please double check that it has correctly updated
`core/public/version.h`, `tools/pip_package/setup.py`, and
`tensorflow/tensorflow.bzl`. Also review the execution notes below:

```
Major: 2 -> 2
Minor: 15 -> 15
Patch: 0 -> 0

No lingering old version strings "2.15.0-rc0" found in source directory 
"tensorflow/". Good.
WARNING: Below are potentially instances of lingering old version string 
"2.15.0rc0" in source directory "tensorflow/" that are not updated by this 
script. Please check them manually!
tensorflow/tools/pip_package/setup.py:120:2.15.0rc0
tensorflow/tools/pip_package/setup.py:121:2.15.0rc0
```