I will try to reboot when I'm home but initramfs seems to be quite light... maybe it's normal.
-rw-------. 1 root root 64M 18 juin 18:32 initramfs-4.0.0-1.el7.armv7hl.img -rw------- 1 root root 33M 24 août 14:23 initramfs-4.2.0-0.rc2.git0.1.centos.el7.armv7hl.img
Mine's 29MB The reason the older (initramfs-4.0.0-1.el7.armv7hl.img) one is bigger is because earlier, RBF used to generate initramfs using the option --no-compress