I know what you mean about feeling different by not crying. My grandfather died when I was a sophmore in high school, my 21 year old cousin 4 months later. Then a 38 year old aunt a year after that.
I didn’t cry at any of their funerals, or at any other point concerning their deaths. I started to wonder, am I that selfish? Am I that calused and uncaring?
I actually prayed to become more emotional. I analized it quite a bit. I thought about how when I was younger I had learned to ignore the constant insults of bullies or my older brother. I completely tuned them out, never getting angry or worked up. This analizing in highschool got me starting to worry I may have shut off some emotion center in my mind. Or another worry was that maybe I was distancing myself from everyone and thus didn’t care when they died.
I can’t tell you I had a definitive answer or ever “rectified this problem”. I’m now 25, with a wife and a child on the way. I’ve cried a couple times since high school. Twice really hard, once when a good friend died and I was trying to express to his parents what a great person he was (they ended up consoling me instead

) And a second time when I was dumped by a girl I dated for 10 months, even though I knew that we just we would never work out and planned to dump her soon.
But besides those times, I’ve not really very cried. On the flip side, I don’t get too excited either. When my dad suprised me by giving me a car after graduating high school, I said, “Wow, thanks.” in a very genuine but calm manner. Very worried, he asked, “Do you like it?” And I did, I’ve put over 100,000 miles on it, and still drive it - but I’m not the type to jump up and scream.
I say all this to say, I have full confidence that I have nothing mentally, spiritually, or emotionally wrong with me - and I seem to share the symptoms that you describe.
For me, I attribute it to being extremely analitical. I analize a situation, judge good/bad and decide. My wife loves it, she is a worrier. She has losts of emotion (up and down) and second guesses alot. She appreciates that I can be a sort of rock to cling to when things are hard.
On the flip side being analitical means most of the time when I sin, it’s premeditated and thus mortal. And I can be stubborn about things I’ve already answered b/c I looked at the facts and decided - why rehash?
I suggest just trusting your high school and college years learning about yourself in the same way I was able to. Learn what gifts you have and where you are lacking - then work on maximizing the former and improving the later.
You’re 15, at that age it’s normal do doubt that you are normal (ironic isn’t it). And it’s normal to not fully understand your personality b/c it’s still in high development. Stive to be a saint now. Make as many good habits as possible now. Trust God built you well now. Then looking back even as young as 25 you’ll likely look back at the you from 10 years ago and think, “What a great young woman, I’m glad she strove for virtue allowing me to become who I am”…and all the worries about ‘being normal’ or ‘where are my emotions?’ will just put a little smirk on your face and you’re think, “There weren’t any problems, that’s just me.”