4 (Carretera #4),[3] is a main highway connecting the municipalities of Guayama and Cayey in Puerto Rico.

[1] This highway consists of one lane in each direction for most of its length due to its rural characteristics.

[5] In this municipality, PR-15 makes its way though Caimital, Palmas and Guamaní barrios before entering Cayey.

Between Jájome Alto and Culebras Bajo barrios, PR-15 meets with the Ruta Panorámica, of which is part from PR-741 intersection to PR-7737 junction.

[7] After that, the road goes down the mountains through Quebrada Arriba and Monte Llano barrios until its junction with PR-1, where PR-15 enters the city center for make its final length until PR-14 intersection.