Instead of doing the same exercises every day, you would benefit more from giving your muscles at least one day of rest before working the same muscles every day. This concept is known as a "split". You work certain muscle groups on certain days and manage your recovery accordingly. Muscles have the chance to improve during rest, exercise is the stimulus and too much stimulus can interfere with or even be detrimental to growth (the biggest sign of too much would be getting weaker).
So what sort of split should you try? I think that a "bro split" where you only work a couple muscle groups each day would work best if you only have 15 mins. One potential example of what that might look like is a Chest and Shoulders Day, a Back and Glutes Day, a Biceps and Triceps Day, a Quad and Hamstring Day, and a Calf and Forearm Day. Alternatively, a Push/Pull/Legs split might work better if you have more time. Your core (abs, obliques, etc) can be done any day, it recovers quickly and can be worked on the same day as another workout or on its own separate day(s).
When doing any kind of strength training, it's important to give yourself an appropriate challenge. This can be manipulated in a variety of ways, weight, exercise selection, speed (rep cadence), total reps, range of motion, etc. In general though, working to (or close to) failure is a good indicator that you've pushed yourself enough within an individual set. Popular set and rep counts include 3x10 and 5x5 (sets x reps), but the exact number of reps is secondary to reaching that appropriate challenge (to or close to failure). Just pick a weight that sees you reaching that challenge at whatever set/rep count you decide to go with.
However, you're really limiting what you can do with just two 8.5 kg dumbbells that I'm only assuming are adjustable. That's not to say that you can't get a good workout, simply that you should look at expanding your options in the future to better make use of your time and efforts. Most notably it's going to be hard to challenge your legs with so little weight. You'll probably want to focus on single leg variations of exercises for that reason, Single Leg Squat, Single Leg RDL, etc. For other things, just look online for dumbbell options for specific muscle groups. Here's a YouTube playlist with some options for you.
Now what is an example of what this would look like in practice?
Monday - Chest and Shoulders
- DB Flat Bench Press - 3 sets of 10
- UCV Raise (Example in Video) - 3 sets of 10
- DB Shoulder Raise - 3 sets of 10
- Rear Delt DB Row - 3 sets of 10
This should take approximately 15-21 minutes with a rep cadence of 3-5
seconds and 60 seconds of rest between each set.