If you're operating the radio in normal trunked mode of a single trunked system as an authorized user, then you want to use Priority Monitor scan lists.
You're not going to be able to scan more than 15+1 talkgroups at a time with an XTS, though.
Scan lists are tied directly to the trunked personality, which is then tied to a channel in a zone. In other words, only one scan list at a time is active, and that scan list is determined by what channel the radio is on, which then references the trunking personality to see which scan list to enable. You as the end user cannot change scan lists via the radio's interface, nor will the radio magically scan more than the 15 channels that are in the scan list assigned to the personality.