If you ever saw two official PS2 memory cards for $15, it sure wasn't MSRP. The price of such a thing would've been more like $40 normally and $30 on sale back then.
$15 has been the MSRP for years now for just a single official PS2 memory card. And it used to be $25.
And if you want your saves backed up, there's the cloud save function that will do just that.
All four major console's presently on the marketplace do just that.