The iron chalcogenide Fe_{1+y}Te_{1-x}Se_{x} on the Te-rich side is known to exhibit the strongest electron correlations among the Fe-based superconductors, and is non-superconducting for x < 0.1. In order to understand the origin of such behaviors, we have performed ARPES studies of Fe_{1+y}Te_{1-x}Se_{x} (x = 0, 0.1, 0.2, and 0.4). The obtained mass renormalization factors for different energy bands are qualitatively consistent with DFT + DMFT calculations. Our results provide evidence for strong orbital dependence of mass renormalization, and systematic data which help us to resolve inconsistencies with other experimental data. The unusually strong orbital dependence of mass renormalization in Te-rich Fe_{1+y}Te_{1-x}Se_{x} arises from the dominant contribution to the Fermi surface of the d_{xy} band, which is the most strongly correlated and may contribute to the suppression of superconductivity. Show Partial Abstract