I didn’t have that issue, but you could try changing kodi.sh to
#!/bin/bash /opt/retropie/supplementary/runcommand/runcommand.sh 0 "startkodi" "kodi"
And see if that makes any difference.
I think you have to uninstall kodi 14 first (at least according to the post I used to install it- but they were saying to make sure you install kodi 14 first so you have the right dependencies and then you uninstall it before you install kodi 15.) You could try it without uninstalling it and see if it works, but I uninstalled 14 first when I installed 15.