Kole and Naso QT Help

[Reef23]

Hey all,
I went to have a peak at a yellow eyed kole tang (3.5") today and confirmed he was fat and healthy. I setup my 15G QT tank before I left. I will be picking him up next week as I will be out of town for the next few days. Problem is I fell in love with a blonde naso tang (2.5") while i was there as well. Im in the process of upgrading from my current 75G to a custom miracles 145G. I was going to QT the tang for 3/4 wks(new tank will be plumbed in the next few weeks). I know the naso will out grow my tank but I have plenty of friends with large tanks that will be happy to take him as soon as I notice stress or aggression. My problem is how can I QT both of these guys ? Will they both be ok in a 15G QT tank ? Do you guys normally treat a fish with medication even if there is no sign of illness ? What medicine if so ?
Thanks