You could try booting your system into the Leap iso, and proceed with the installation process. It should detect your current partitioning, and see if you can choose not to touch your home subvolume.
But I would strongly suggest to backup your home data, and do a fresh install. I have not tried this recently, but if your system is UEFI and have secureboot enabled, the installation media may not be able to boot due to the installed shim should be newer than the one on the iso.