How do you play 15–20BB?

One stack size that I sometimes have trouble with is around 15—20BB.

For now, I still have enough chips to increase my normal bet and play postflop, but I also don't want to lose too much stack in difficult situations.

Do you prefer to play more attacking push/fold at this stack depth, or still open your cards normally and find good postflop positions?

Personally, I usually become more attacking at the end, especially when the players behind me are pretty solid.

Which method suits you best?

With 15–20BB, I think you have to be more proactive rather than waiting for premium hands.
I’d look for good spots to steal blinds and use position, while avoiding marginal calls that eat into the stack.
Once you get closer to 10BB, I’d be much more willing to take the push/fold route.

I prefer to play more aggressive with a low chip than raise a mini raise and take 3 medium card calls and end up losing to hands that wouldn't pay all in

Very tight always so when I decide to bluff they do not see me coming.

With 15-20BB its often more advantageous to rejam over an open instead of being the player opening and allowing others to rejam on you. Especially small pairs often need to be open folded with this stack size, because they play poorly, when someone call, and they dont block rejamming ranges. And in general if you have aggressive rejammers behind, its often better to open fold hands, that you dont want to call off with. Without aggressive rejammers behind you can still try to play some "small-ball" and steal some blinds, maybe fire a C-bet on the flop, if BB defend, then give up if he continue etc.

Good question happens to me a lot that blocked me in those situations