  We study models with heavy exotics that account for the LHC $750$ GeV
diphoton excess in light of current vector-like quark bounds. Utilizing only
exotics that may appear in three-stack and four-stack D-brane models, we show
that a narrow width diphoton excess can be accounted for while evading existing
bounds if multiple exotics are added, with vector-like leptons of mass
$M_L\lesssim 375$ GeV and vector-like quarks with masses up to $\simeq 3$ TeV.
However, a large width $(\Gamma/M \sim 0.06)$, as suggested by the ATLAS data,
cannot be easily accommodated in this framework. Renormalization group
equations with GUT-scale boundary conditions show that these supersymmetric
models are perturbative and stable. Type IIA compactifications on toroidal
orbifolds allow for $O(10)$ Yukawa couplings in the ultraviolet.
