Running 4k in 25 minutes is not fast! This speed is fine. But everyone's speed is different, and with weight loss in mind, it's something you try to stick with for as long as possible, like 1 hour or 90 minutes, or longer.　

How slow is slow, in terms of your speed? It's fine if you don't talk too hard when you're running!

The big breath means you're running hard, and breathing through your mouth can easily lead to a fork in the air or something, it's the wrong way to run, you should run without your mouth. You're not used to it at first, so you can inhale through your nose and exhale with the help of your mouth.

25 minutes, look at some of the data to say, that can not lose weight, the first 40 minutes to consume your sugar, consumed before calling the body fat burning. So be sure to extend gradually and moderately

PS: Remind the owner to buy a pair of good running shoes that fit you. Garbage shoes will make you run crippled.