Regarding SM Cath runs, i think i done over 200 in the past.
I have a mage myself in one acc, and several chars on other, and u must already figured what happens :P

That drawing is an exact copy of what i did/do in SM cath with my mage.

I also tried with arcane/fire and full frost spec, and from my pov, arcane/fire is a lot faster, based on a fast paced mob pulling and strong aoe damage.
Frost in the end is all about control, and get all those mobs in line, frost nova, blizzard, etc, its just too much time.
u gotta be 70, or at least near it, about 7.5khp and 10k mana self buffed. i have 1100 spell dmg, so anything lower than 750, i think it will just ruin how fast u can nuke them.

Record was 10 minutes sm cath, ice lance pulling, some arcane explosion, frost nova, cone of cold and blast wave. Oh u know the drill right :P ?
Another record was lvl30 to lvl40 in one night, 12hours and 30 minutes, and for me at least, it's was more of a mental accomplishment than just level. i really focus on getting 40 that night :P

Anyways, less than lvl70 mage with less then 750spell dmg +/- it's just going to take far more than 15/20 minutes.