The 15th century in the Spanish territories would be quite a late date for this, as it is a moment of transition, with a nobility that does not live in their fiefdoms anymore, but rather frequents the entourage of the Royal Court. This element was absolutely capital in getting commissions, and also getting rewards and new fiefdoms. When you mentioned "a very wealthy nobleman who owns 15 villages", of course one name came to mind: the Marquess of Santillana.

Don Íñigo López de Mendoza, marquess of Santillana, held enough fiefdoms that every one of his sons received some jurisdictional lordship. The list is positively ludicrous, so I will just name a few of them: Guadalajara, Hita, Buitrago de Lozoya, Fresno de Torote, Monedero, Uceda, Manzanares el Real, Santillana del Mar, the lordship of La Vega (about half of present day Cantabria), Pastrana, Tendilla, Coruña del Conde, Saldaña, Carrión de los Condes, Mendoza, and a surprisingly long et caetera.

This man not only was an aristocrat with a staggering string of holdings, but a man of many talents, being an accomplished diplomat, a qualified general, and a fundamental writer for the history of Spanish literature. It is this last aspect that may allow us to get into his possible contact with his vassals and/or underlings.

He was the son of Diego Hurtado de Mendoza, admiral of Castile, a man who was not always around the Court. Prior to the Enríquez admirals, the Admiral of Castile had to actually manage the diffrent aspects of the fleet, and frequently engage in actual maritime activity, unlike with the later admirals, which basically had a fancy title. However, his father died when he was very young, and he was first raised by his grandmother, and susbsequently by his uncle the archbishop of Toledo. After that, he went to Aragon to serve, as was customary, as page for higher-ups, namely the kids of the royal household. He would eventually come back to Castile, where he became a high ranking man of the Court.

After the battle of Olmedo, he was created Marquess of Santillana and Count of Manzanares el Real, and the titles and honours would keep piling on after that, to the point that he became the most important aristocrat in the Iberian Peninsula, with over 30,000 vassals and an yearly income of over 50,000 ducats.

This marquess of Santillana had close ties to the region of Cantabria he lorded over, and enjoyed visiting the territory due to its healthy air and fertile land. Of course, the land was not the only thing he was interested in, as one can learn from his poetic compositions, most notably his serranillas, where more than once he compliments the beauty of one commoner woman or the other, which means that at some point he must have had something to do with the feminine sector of his serfs or vassals. That point was a constant throughout his life, as good old Gonzalo Fernández de Oviedo notes in his Batallas y Quinquagenas, commenting of the marquess' capital vice being his penchant for women, both common and noble alike, even in his late years.

His fiefdoms being massive and scattered throughout the whole Crown of Castile, naturally means that some of those places never even received a single visit from the marquess. So, a serf from Uceda may have only heard of his lord, never having seen him. A serf from Santillana, on the other hand could have reasonably well have had the occasion of personally meeting don Íñigo, as he was in the region rather frequently, and there he exercised his duties as the top officer of the Crown in the Lordship of La Vega, which meant, among other things, having to act as judge in the legal disputes of the zone.

However, noblemen with plenty of fiefdoms left and right would only known some of the places by name, never even once in their lifetimes visiting those, like Gonzalo Fernández de Córdoba with his Italian holdings of Sessa, Terranova, and Andria. Gonzalo the Great Captain was not an exception, the same was true for the Ulloas who lorded over Villalonso and La Mota but actually resided in Seville, the Arias de Saavedra lords of El Viso residing in Seville too, or the dukes of Medina Sidonia living in Sanlúcar barely even caring about some of their fiefdoms. So, in general, a large feudatary was unlikely to have any actual contact with his actual vassals, being normally involved in the affairs of the royal Court.