Is neither the correct device, nor has it any chance of actually working (missing kernel, just the rootfs, flashing that would brick the device). AP147 is the codename for one of QCA's reference designs/ devboards, while your Letv LBA-047-CH might be similar (based on this reference design), there will be differences (at least the flash partitioning, ar71xx could auto-detect that to some extent, ath79 cannot) which will break the idea.
I am trying to sysupgrade with the snapshot image. But sysupgrade rejects since the device name does not match. Is it fine to proceed with -F (force) in such case?
root@OpenWrt:~# sysupgrade -i -n openwrt-ath79-generic-letv_lba-047-ch-squashfs-sysupgrade.bin
Image not in /tmp, copying...
Device ap147-010 not supported by this image
Supported devices: letv,lba-047-ch
Image check 'fwtool_check_image' failed.