15000 XP every 10 minutes is very slow xp, a duty mission really does give a lot more XP than this, and no waiting for respawns either, you should be able to earn at least 250,000 XP per hour doing duty missions, the only faster xp that i know of is in naboo space, where there are a number of tier 5 ships that are on a fast respawn, but you need good skills to farm them, as they use missiles. as each of the last tier of skills needs 1 million XP to level up, personally i recommend the duty missions, and a decent entertainer buff - xp bonus, precision, critical strikes. etc. If you can't handle the last tier ships solo (any decent pilot should be able to though) then enlisting the aid of another pilot is definitely recommended.