I checked the source code, in /usr/share/usb-creator/usb-creator-helper:InstallBootloader() we should perform s/syslinux_exe/syslinux/g and s/syslinux_var/syslinux/g , after that I can 1) burn 15.04 ISO on 14.04.2 host and 2) boot into the syslinux menu with the usbstick.
I checked the source code, in /usr/share/ usb-creator/ usb-creator- helper: InstallBootload er() we should perform s/syslinux_ exe/syslinux/ g and s/syslinux_ var/syslinux/ g , after that I can 1) burn 15.04 ISO on 14.04.2 host and 2) boot into the syslinux menu with the usbstick.