What about consolidating your travel with one airline?

15K miles/year spread between 2 airlines is pretty inefficient.

Let me share just a short story. Last year at this time I had maybe 19K miles in my AA account, 40K lifetime, 30K in LH and 40K in DL. Never had status on an airline. I thought this year I would fly mayber 35-50K miles, which is more than I have ever flown in 1 year in my life. I commited all of the travel I could to AA and thier partners. Due to a huge uptick in business travel, a couple of family emergencies and my planned travel I wound up flying 115K miles in 2009, if you include last December in the tally I did 143K in the last 11 months. Believe me, around this crowd that is not a large amount of flying!
Thanks to some promotions and a mile run I finished this year with 275K miles in my AA account, 315K lifetime, all but about 10K from flying.

I'm not suggesting that you go hog wild flying around the world, but focusing you efforts on one airline will help you get your to your goals in a couple of different ways ways (and I'm going to speak from an AA perspective)

-the obvious of all flown miles going into one account
-the ability to take advantage of promotions, like double elite qualification miles etc. If you happened to fly you 15K miles during that promotion you would have Gold status which would get you free luggage, 25% mileage bonus on all AA flights and lots of other bennies

Had I not focued I would have missed out on tons of promos and had my miles scattered around 3 or more airlines. Now I am approaching the point where I can take my DW on an around the world trip in Business Class instead of thinking about a free domestic in coach.

By focusing and following some of the advice others give you here you very well may get your every 18 month domestic trip in 1st, instead of coach, and then you will be ruined for life!