If you are learning about DNA, there is an interesting article in the MyHeritage Blog that you might want to read:
“It comes as no surprise that when two siblings are DNA tested, their results will usually be similar. What is surprising to many people, though, is how two siblings (not twins) with exactly the same parents and ancestors can receive different ethnicity results. After all, identical ancestors should give identical ethnicity estimates, right?
“Well, it’s not that simple. In fact, it’s rather common for siblings to have different ethnicity estimates. There are several factors that can affect genealogical ethnicity. We’ll take a look at those factors here.”
Also, if your DNA results say that you have 15% Irish ancestry (or any other ethnicity), You should interpret that as being ABOUT 15%. Ethnicity tests are not super precise. A second text by a different company might say 12% and a third test by a third company might report 22%. Ethnicity report are ALWAYS approximate. All three reports from the different testing companies will be correct.
You can read all about this at: http://bit.ly/2LoN9TA.