Jun: On top of that, the kitchens in studio apartments are apparently not made for cooking. They are always way too narrow and inconvenient to cook in. There are only a tiny sink and an electric stove, and hardly any space to cut foods or put them on. The only food I can cook in there is cup noodles.
Kay: And maybe pancakes, too?
Jun: Yeah, if you try very hard. I bet those small kitchens definitely shorten the average life span of the Japanese.
Kay: Aren't you exaggerating, Jun? That sounds somewhat possible, though. soa natural?

‎Jun: On top of that, the kitchens in studio apartments are apparently not made for cooking. They are always way too narrow and difficult to cook in. There's only a tiny sink and an electric stove, and hardly any space to cut food or put it down. The only thing I can cook in there is cup noodles.
Kay: And maybe pancakes, too?
Jun: Yeah, if I try very hard. I bet those tiny kitchens shorten the average life span of the Japanese.
Kay: Aren't you exaggerating, Jun? That does sound possible, though.

*inconvenient is a great word, but it sounds like an understatement here. I think what you mean is that it's hard.
*can't use "I bet" and "definitely" together. I bet is like 80% sure and definitely is 100% sure
*there's nothing wrong with "small kitchen" but I think tiny sounds better and it's more clear that the kitchens are too small, not just that they are slightly small.