When I am driving on a busy city traffic slowly at about 15-20 kms/hr in 2nd gear and I realize I have to slow down / stop .
I can take off my foot from accelerator, and
1. Fully press the clutch. As speed decreases, car will gradually stop (and I may apply break to bring is to complete rest at right spot). Change gear from 2nd to neutral position after complete stop. Press clutch and change to 1st gear when I want to move and apply gas.
My question is suppose I realize I need not stop fully and need not change to 1st gear. But since I have already pressed clutch, I apply gas and slowly release clutch without changing gear.
Is it OK to press clutch and release it without changing gears. I am aware of riding of clutch but in this case I am not applying gas and only applying brake and clutch.

I could be wrong. I learned to drive a stick shift in an old three-speed mustang. That clutch had to be slipped, all the time. I replaced it once myself, but it was simple. Then, I drove in heavy traffic for 11 years in a Geo Metro before the clutch went out. I did just like you did, I left it in second gear. The less shifting you have to do, the better. My clutch did go out in that car, at a red light. I put it in first, started, heard a "pong" sound and there was no second gear. Luckily, it was already rolling and I just slipped it into a parking space. That cost $700.00 to repair (new clutch) in 2004.

It's important to remember that even if the clutch is depressed, the car is not truly in neutral. It rolls but the engine reacts as if it were in gear. So rolling down a big hill, put it in neutral. I'm a girl who used to do my own tune-ups and car repair. But, I sure don't know much about newer cars. You should ask someone who has had a lot of cars, fixed them and drives a clutch.