My maternal aunt sent me her mtDNA test results.
How can I relate this to my own ancestry?
If her mtDNA falls 15% within a certain country, what percent of my DNA would also fit there?
Your maternal aunt has the same mother with your mother. The mtDNA
It means that there is great probability that you have the same mtDNA with your maternal aunt.
Please don't be confused in questions of differences between mtDNA and atDNA. mtDNA is the DNA located in specific organells of cell called 'mitochondrias'. This DNA is very small and as I said before inherited from the mother. It affects how energy is transformed in our bodies. atDNA is autosomal DNA located in the cell's nucleus. It contains of 22 chromosome pairs and sex chromosomes (XX or XY). They are inherited from both parents and define how we look, feel etc.
You will have the same mtDNA as your maternal aunt - as mtDNA is remains largely unchanged for thousands of years in your direct maternal line. Did you you get information on the Haplogroup? You can read more about these tests here: https://www.smarterhobby.com/genealogy/best-dna-test/