Why does my G6 heat only get hot when I drive it? It does not defrost my windows just warming up

What is your question?

I start my car 15 min before I leave and it never gets hot. I have to drive it in order for it to get warm. But every time I come to a stop it gets cold again. The blower is fine. The heat is fine if going over 70 mph. It is 2006. I can never defrost my windows in the morning.

What makes this problem better or worse?

Better if going over 70 mph

How long has your 2006 Pontiac G6 had this problem?

just had the car since last summer. Did not know it did this.