Linux Mint 18.3 on The MacBook White 3.1

Yesterday updated Linux Mint (XFCE) on the MacBook White to 18.3.
The update, of course, went smooth but, after the update, came the newer kernels.
And that's when the problems started.
The newest kernel (4.15.0-48) works, that is, the lappie does boot and you can use it, WiFi works, etc. etc.
But it took ages to boot, and then, once on the LightDM login manager it also took quite a while to actually be able to type anything and then again it took quite a lot of time to get a working Desktop, once past the login manager.
It was unbearable a true PITA.
What I did was to revert to an older kernel, but it took a while since I wasn't able to access the GRUB menu (via Shift key upon booting) not sure if that was because I'm running an encrypted LVM or waht a hell, but the only option was to boot the newest (and slowest) kernel and then edit the file "/etc/default/grub" and add the option GRUB_TIMEOUT_STYLE="menu" to the end of the file, and then, after a sudo update-grub and a reboot I was able to choose the kernel I want to boot.
Didn't have time to investigate the slowdown for the moment using an older kernel on the lappie let me regain control of it.