Ah thanks for the info. Feels like I started the game too late, seeing all the 90s running around (and killing me when I try to quest, stupid PvP server) and all the flying mounts everywhere. ;__;
You can do the random for lowbie dungeons at 15, but that's different from raid finder. Those give quite good exp since they are so easy to run through and almost all of them have quest givers that one run through will complete, but i would quest in-between dungeons until the next one is available. The exp from dungeon finder drops a lot if there's not quests supplementing it.
Heirlooms are great too but the only way to get those without a max lvl toon is through guild rep. That is pretty easy to get but those might be pretty expensive for someone with no max lvls to earn money with.