Karms,
Try walking a little further each day. 5 km a day or 2.5 each way isn't really enough to bring out any problems. You want to do 2 things, improve your overall fitness and find out if there are any problems. Better to find out at home where you have a chance of fixing them than somewhere in Spain. You can only find out if you going to have problems by walking the extra distance.
When I started walking to prepare for our camino this spring, I ran into problems at about 10 - 12 km. My feet were killing me and my legs would shake with exhaustion. The foot problems I solved with orthotic inserts and the fatigue by losing weight and exercise. On weekends, weather permitting, I now walk about 16 km each day and my goal is to be able to walk 25 to 30 a day. Your weight sounds fine and you are half my age. I was 25 kg overweight, now I'm 15 and planning to lose as much more as I can. I'd like to lose the age but I'm stuck with it. I have plantar fasciitis in both feet and osteoarthritis in my knees, hips and spine, nothing really serious, but very painful at times.
It takes serious and ruthless planning to get your pack weight to 5 kg or less. Fortunately, ultralight backpacking is very popular now and there are lots of resources on the web. Try searching using ultralight backpacking gear as keywords. The good news is that with the lighter pack weight you can use a much lighter pack, a rucksack rather than a frame pack. Because the weight on your back is so much less you can wear lighter shoes rather than heavy boots (but do make sure you have good ankle support). When planning, don’t forget to include the weight of the water and snacks that you are carrying but don’t include the weight of what you expect to wear. My daughter and I will be carrying a base gear weight of 3.5 kg each with a total weight including water and snacks of about 5.5 kg. There are some ultralight backpackers who, including their tent and sleeping bag, carry 2.5 kg base gear weight although the average seems to be 5 kg. Since we don’t need a tent or cold weather sleeping bag, 3.5 was easy to achieve.
I hope this helps. Good luck and buen camino.