Hi,
I was going to say that, unless you were using the Batch dimension, you can't. But then I did a quick test.
If you have a non-Batch item, and no special setup on the Item model group, then AX will reserve inventory in Location ID order.
But if you tick FIFO date-controlled on the Item model group, it behaves differently. For example in the scenario you give, it behaves exactly as you describe. However, if, for example, LOC-2 contains the receipt from the 7th and then a fourth receipt from the 15th, AX will reserve LOC-2 last, not first.
So, for the ultimate solution, I think you should consider using the Batch dimension. If you can't use Batch, for something close, but not perfect, test the FIFO date-controlled parameter.
That parameter is describe a bit here (but is referred to simply as Date-controlled).