DR is at rank 10 , lvl 15 is Zadnor
but yeah u get tons of clusters on your way to 10 (free from quests even)
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I did. I only join groups in CE's and leave them once they are completed. For leveling I was just running skirmishes solo. The few clusters I got were spent on the mount speed increase for Zadnor. (Still missing the one for Southern front though)
So yes it's absolutely possible.