Get candy faster

I suggest using only major healing potions for the first round, while directing yourself to the parts where the demon clusters are the thinnest. Use a major healing potion as soon as the cooldown is over, especially at the wall. What you want to aim for are single demons. Don't be afraid to hit those, since you have more than enough HP to survive.

Once you get teleported back, go to the bottom row as soon as possible and summon an imp. It will kill the ghosts as well as eat through a wall. On your final teleport back, go to the bottom row again (avoid fireballs whenever necessary) and summon another imp, which will cut through the hoard of ghosts to the demon. Use invincibility and spam fire scrolls, and you should be done.

Each 15 minutes, the stock is updated by this formula:

this.setNbrInStock(this.nbrInStock + 15 + random.getRandomIntUpTo(10));

It adds 15 plus a random value between 0 and 10 of LPs to the stock. The maximum of LPs in stock is 140.

The update will occur, no matter whether you buy something or not, it just will be 140 LPs max.

if(this.nbrInStock > 140) this.nbrInStock = 140;

Funfact: It seems, that originally, it was planned, that the maximum are 100 LPs, as the comment says If > 100, decrease it.