After the LE installation you'll start with an untouched "guisettings.xml", which seems to work fine. After the first boot the "guisettings.xml" will be updated with a "videoscreen.whitelist" (see XML tag inside the file) fitting to your screen. I think that process fails.
To test my theory, do this:
- make a fresh LE installation on MicroSD
- copy the untouched "guisettings.xml" from MicroSD to your PC
- boot the RPi with LE
- power off RPi by shutdown menu
- remove the MicroSD card and plug it into your PC
- copy the potentially corrupted "guisettings.xml" to your PC (verify it, and maybe post it here)
- replace it by the untouched original
- try to boot the RPi again
It could end up having a DE-15 <---> HDMI issue.