Yes, the Spanish were less averse to mixing with the local population than other European peoples such as the English and the French. What is the percent admixture in that 15-20% that have African ancestry and is that Northern (e.g. Berbers) or sub-Saharan? The Boers, for example, have slight African admixture, presumable San and Zulu, but it is slight making it almost imperceptible. Do you have a link to that study?The racial delusion in Argentina was a germanic influence in the 30´of the XX century whose example to follow was Australia (see Macri´s speeches and plans: https://www.lanacion.com.ar/sociedad/de-la-economia-del-avestruz-a-la-del-canguro-por-que-no-somos-australia-y-que-necesitamos-para-serlo-nid2242557/) because, as a former colony of Spain, the policy was always the integration of the local populations. The same happened with former slaves. I posted some months ago a study that showed that about 15 or 20% (I do not remember) of its population has African gens.
In my personal case, I have Italian, French, Russian Jude, Polish and native american (mapuche) blood. My children has to add Chinese and Korean blood.