Believe me, if you do interval training on a treadmill, you will feel it! A good high intensity interval routine is very different to being on your feet all day. I mentioned walking on the treadmill because you say in your OP that you are overweight. So running at this point is probably too much for your joints. But an example of what I do is to set the treadmill incline at 2.0 and the speed at 6 kph - a brisk walk. On every minute, I put the incline up by 1. So by 10 minutes in, I'm walking at an incline of 11 or 12. It is tough!
If you didn't want to be on the treadmill, you could do something like that on a stationary bike.
Set the resistance at somewhere between 8 and 10 (start lower), then pedal like fury for 30 seconds - try to keep your RPM at over 80. Then slow down for 30 seconds, then speed up.
And so on. 10 minutes of that will get your heart rate up, without too much load on your joints.
See how you feel - if you are really really exhausted - lower your speeds and resistance. But it should get to be really tough - I'm very fit, and when I do that sort of interval training on a bike (I put resistance at 12, and I try to keep the RPM between 90 and 100), I work till I feel my legs won't hold me up!
But it's only for 10 or 15 minutes. 10 rounds, and you have a rest between each maximum effort.
It's not the only kind of training to do, and weights are transformative! (I started lifting free weights heavy 4 years ago and compound lifts - deadlifts and squats - are fantastic all body exercise!) But you need to do some cardio training, and HIIT is really good for this.
To really get your fitness level up, it's probably far better to do 15 minutes of cycling/walking/running intervals, as fast as you can, than 45 minutes steady state of the same exercise.