My pecs are growing slow but my arms fast?

I'm 15 very soon 16, and when I started around 5-6 months ago hitting the gym, my pecs were basically none existent at the time. I have developed some muscle in my chest but not even close to what I would call ok. The thing is my arms are gaining muscles just fine, sometimes I even see people with really nice looking chests but they have smaller arms than me. I do push/pull with a leg day. 5 times a week a good 1.5-2h each time. My routine normally looks like this,
Monday: Legday
Tuesday: Push
Wednesday: Pull
Thursday: Rest
Friday: Rest/Push
Saturday: Push/Pull
Wednesday: Pull/Rest.
On push, I even do specific chest exercises. I would say I eat well. Good amount of meat, fruits beans etc.. Even asked my dad and my friends about how I should eat (my friends have done more research on the topic than me). So I doubt it would have anything to do with that. Am I doing something wrong/is there something I should change? Or is my chest just a slow grower, if so will it start to grow faster over time?