Hello Yuri,
i checked the Dutch coins from the nineteenth century and the only one that fits 15 mm is a Dubbeltje (10 cents) they where made in silver.
https://en.wikipedia.org/wiki/Dubbeltje
I also checked the coin sizes from the VOC but they where larger and even the coins from Indonesia during the Dutch era see the picture here it is 1/10 of a Guilder.
Maybe this might be a clue.
Regards, Martin