I suggest that you create one product and its variants in Odoo

Then export that product with all relevant data, including variants data to a csv file(Utf-8/,)

open the csv file(Utf-8/,)

add only a second product to the csv file(Utf-8/,) with its data that must match with the 1st product lines

save the file and import it into Odoo; if this works then

add the 15998 other products to the csv file(Utf-8/,) with their data that must match with the first 2 product lines 

save the  csv file(Utf-8/,)

Reimport the csv file after deletion of the fist 2 product lines (to avoid duplication)