Hello, I'm 15 and I have a 4.5 inch (erect) and 5.3 inch (thick) penis and I'm in the tanner 3 stage. I haven't grown in height much and my penis has only grown like 1 inch erect, I wonder if I'm going to grow more? Is it because I possibly have low testosterone or GH?
For a 14-15 year old 4-5" erect is average. You're in the range.
Most males have a growth spurt between about 15-16 or so.
Your penis can grow into your early 20's.
I doubt you have low testosterone. Give it some time. We don't all develop at the same rates/times.