You can basically use what ever fiters you want to use, however, if you use carbon filters, know that if you end up having to add medications to your QT to treat sick fish, that the carbon will need to be removed.
Also, you shouldn't add any substrate. The tank should be bare bottom and either painted black or blue on the bottom [outside of tank] or placed on a dark tabletop. The reason for this is because sands absorb medications and would render any medications that may need to use in the future, less effective. As for LR, while you can cycle the tank with live rock, once you plan to add fish, the LR should be returned to your main tank. Again, the medication issue, but, also, if you use hyposalinity in your tank, lr will not tolerate hyposaline conditions.
15 gal tank sounds like a pretty good size. Remember, when QT-ing, for the most part, you want to QT only 1 fish at a time. The exception to this would be paired fish, or schoolling fish.
