Only you can decide what is best for you. The aforementioned cost of ammo is a consideration. The days of the 30.00 200 round battle packs are long gone.
The rifle is costing you nothing to keep.
You can piece together your AR10 as funds allow without selling.
What if the SHTF arrives and you want the Mrs or kids to have a weapon? A 15 is going to be lighter and easier to handle for someone that is not a dedicated shooter. If you are on the move you can carry a third more ammo with 5.56.
Look at a toolbox- do you just want a crescent wrench in there or do you want the correct tool for the job at hand?
One last thought-looking down the road if you do sell- will you be able to replace it? I think a nasty AWB is in our future, especially if Oblunders ATF nominee (Andrew Travers) is seated as the Executive Director of BATF. No, he cannot make the law but if you think he would not have influence think again.

I vote to keep her...