It seems to be an iPad Mini 1 (MD529LL/A), with about 25 GB of free space. I'm afraid it might be the fact it is an old model, but since I restored it to its factory settings and then lowered all the performance consuming options, I hoped for a better outcome. After several attempts, nothing worked, I think the solution…
But there's still no improvement in the performance of the usage of my King Apps, BubbleWitch2 and Papa Pear keep crashing after a couple seconds of being opened, I can't even make it to the levels screen.
I have tried everything and nothing works so far, I can't even join the forum because of the laggy iPad interface (I now used my iPhone to fulfill that).