These number still seem a bit high (probably due to the large age range). I have recalculated the percentages using the correct age range (25-65):

• 6.05% primary education
• 14.04% lower secondary education

And because we all like to see the actual data (2019, everything is x1000):

25 35 45 55 25-65
2189 + 2030 + 2459 + 2323 = 9001 # total
74 + 95 + 155 + 221 = 545 # primary education (ISCED level 1)
120 + 132 + 241 + 315 = 808 # lower secondary education (ISCED level 2)
73 + 84 + 130 + 169 = 456 # lower secondary education cont.
26 + 40 + 47 + 43 = 156 # unknown

For each level % out of total:
6.05%
8.98%
5.06%

For a total of 21.83% with ISCED level 2 or less in the age range 25-65.

Source for ISCED levels: The Structure of the European Education Systems 2018/19 - Eurydice - p.24.

Source for education data: https://opendata.cbs.nl/statline/#/CBS/nl/dataset/82275NED/table.

Source for age data: https://opendata.cbs.nl/statline/#/CBS/nl/dataset/7461BEV/table.