Getting to 15 in any crafting class should be relatively cheap. You are not subject to the whims of the Marketboard, only the fixed costs of NPC vendors in the various guildhalls.

Just make everything in the 1-5, 6-10, and 10-15 crafting logs once. Depending on experience bonuses (are you Rested? Eating food? Getting a lot of Quality added to your recipes?) and the size of the crafting logs you should hit 15 in most (I think either Armorer or Blacksmith was the one I did not) before finishing those crafting logs. In that case, just pick something cheap and spam it until you hit 15.

Progressing higher than 15, though, you are likely going to want to start leveling your gathering classes as well, to cut the cost of materials on the marketboard.