Comment # 4 on bug 1187859 from Adrian Schr���ter

you do wild mixes of repositories here, please note that the standard repos in
SLE are usually empty and just include further pathes. However, only the last
entry gets expanded. 

So just simplify your config eg with

  <repository name="SLE_15_SP3">
    <path project="Kernel:SLE15-SP3" repository="standard"/>
    <path project="SUSE:SLE-15-SP3:Update" repository="standard"/>
    <arch>x86_64</arch>
  </repository>

and let OBS expand the path elements. Otherwise you would really collect all
module repositories on your own.

and btw, you can debug this using 


 osc buildinfo ...

no need to wait for a build.