Personally, I would go with 2 x 8GB... giving you 24GB of RAM, which is plenty
I've been dealing with these guys for years and FedEx delivery of RAM is fairly cheap and very fast to me in Australia, should be similar to you in Belgium
I'd get a set of Crucial ram if I were you. They are found at really good prices in Amazon UK, should be a couple more days to ship to Belgium. Much better than a long time ordering from USA plus risk of taxes and no customs as you're in the EU. Make sure they're DDR3L with 1600 MHz speed.