10-15 minutes of playing for a day is no where enough when you're learning. Do clean the horn as instructed in here even if it's new. You have no idea where or how long it was sitting somewhere. I bought a piece of crap online (new) and upon inspecting it, I found rust on the valves etc. Don't ever believe everything in an ad or online site etc. You should also be asking your teacher what to practice as far as scales. I think he's an old guy and should retire already, so he just instructs you on the minimum of what to practice. Just cause he's your teacher does not make him a trumpet GOD. You need to practice alot, more than 15 minutes a day.