Ordinarily, 55 liters is on the overly large rucksack size of the Camino rucksack continuum. But, if you have it and it is comfortable to wear for 6-8 hours daily, use it.
Packing for two-weeks on a Camino is near-identical to packing for a month or more. The 55 liters will not be filled with the required kit. However, as you process along your Camino route RESIST the temptation to acquire stuff, souvenirs, more things you do not need.
I like to state that empty volume in a rucksack has negative pressure - it sucks. The normal tendency is to think - “hey, I have plenty of space - no problem.” By the end of your Camino you are a burro carrying way too much.
Just FYI, and FWIW, the “sweet spot” for a man’s rucksack seems to be somewhere around 35-40 liters. For women, it might be 30 - 35 liters, as they typically have smaller clothing. But everyone is unique.
Personally, I started with a 48 liter bag, then changed to the same model In a 38 liter size - to reduce the “just in case” stuff I carried on by my first few Caminos. I am now trying to get it down to 30-32 liters, plus a “belly bag” that attaches to the front of my rucksack harness to balance the overall weight.
Volume tends to equal weight. Weight is the enemy when you are walking long distances.
Hope this helps,
Tom