First time car buying

i just bought a $20,000 car with $5,000 down. I got a $1500 powertrain warranty and $500 GAP insurance, and the dealership had a fee of around $600. I don’t have extensive credit history so i got hit with a massive APR rate of 16%. If it is 16% of the loan I took out (somehow ending up around $19,000), why will I have paid an extra $10,000 in interest? That doesn’t sound like 16% lol. Is there anything I can do to lower that? Am i going crazy or are the numbers really high for a 25% down payment