Are you doing these with a 10kg weight in each hand? I only have an 8kg bar and an 8kg kettlebell so cannot use them simultaneously. Having just gently restarted doing upper body exercise I have managed 1 set of 15 reps on each side - I am taking it easy for multiple reasons - I can remember getting a very sore biceps tendon doing biceps curls decades ago. I am very impressed with your numbers.