Why does portal boss take 33 minutes on my L11 mage? L16 also takes way too long. L43 and L56 was fine enough.

My L11 mage has this gear:
L10 expedition rifle of brutality (+2int +1,5%int)
L11 ancient druid helm of brutality (clean)
L11 rotten spirit shroud of brutality (clean)
L11 silver hoop of brutality (+2int)
L10 tenor's pendant of lethality (clean)

Pets:
L11 slink
L11 korruption

Skills:
heal, ice bolt, gale, timeshift

Stats:
Put all to primary (int)

My end game toon does it in 1/60th the time. Not even exaggerating. Is this intentional? Wouldn't dare go on my L5 mage now, seeing as it takes longer to kill the lower the level on toon is....