pciconf -lv. freebsd-update -r.if_re_load="YES"
if_re_name="/boot/modules/if_re.ko"
ifconfig_re0="DHCP"
env ABI=FreeBSD:15:amd64 pkg fetch realtek-re-kmod before starting the upgrade and save that package somewhere safe. The entire freebsd-update install stages can be done 'offline' but you're going to have a problem with your currently installed Realtek driver once you replace the kernel with the 15.0 version. That driver was built for an older version and will likely fail to load on the new version. It'll get you in a chicken and egg situation. You can use the 'old' pkg-static(8) to reinstall that kernel module (for 15.0) you saved earlier.