i have cheese denim in my collection. Long story short, they are really good. The denim are usually imported from japan, and the machine they use is old machine like singer,  union special. since they made it in house means u can make a bespoke denim tailored to your taste.

for their ready made ones its great too. was banging my head when i didnt get the 18oz ones where the denim was quite rare and hard to find.

As for chinese brand i guess most of what u mentioned are okay. if u are having 2nd thoughts on the chinese brand, hey go for for alternative route such as japan blue or sugarcane. still cheap imho.

Some people can wear 18oz no problem even without aircon.

Depends on you, I guess.

I'm happy with most 15 oz as I feels right for me.

Tried 18 or 21oz b4, feels kinda off for me personally.

But since we are still in lockdown, I haven't wore my jeans in ages