The potion has a recast time of 5 mins, but for a potion with a duration of 15 secs is simply useless. They might as well lower the elemental resistance but to increase the duration, say, increase resistance by 8% with the duration for 2 mins, which I believe may be worthwhile.
Similar problems with some of the buff and debuff spells, with some of them with long recast timer but such short duration. For long recast timer I can understand as they don't want you spamming the spell, but for such short duration, it renders those spells useless e.g. Virus duration is 10s, how many hits will a mob hit the tank during that time....might as well cast damage spells instead.