Am i the only one having problems to slow down?

@Edwards Have you tried very large parachutes?

@yopo i do those at 0% throttle and with airbrakes fully out, and even then, i spent 20 minutes trying to loose enough speed for a landing approach

You can try combinations of flaring maneuvers and repeated sets of long turns left or right while spiraling down in altitude in combination with airbrakes and reduced throttle to slow down to safe landing speeds. That's how real jet aircraft maneuver to slow down to safe landing speeds. Also, the more massive your craft and the more velocity it has, then the more momentum it will have. So, you could try reducing the mass of your craft's parts to make it easier for maneuvers and air-brakes to slow it down. See here: https://en.wikipedia.org/wiki/Momentum

@yopo i did add airbrakes to most of my planes, some massive ones even, like on my last post, but still then, they only seem to make a difference above mach 1

Honestly, I just use a parachute to slow down my planes. It’s very simple and it does a very good job at slowing down. Though the amount of slowdown is a little dramatic as the craft can come off the ground for a second.

Perhaps you could try adding some air-brakes? https://en.wikipedia.org/wiki/Airbrake(aeronautics)