  We discuss various modified dispersion relations motivated by quantum gravity
which might affect the propagation of the recently observed gravitational-wave
signal of the event GW150914. We find that the bounds set by the data on the
characteristic quantum-gravity mass scale $M$ are too weak to constrain these
scenarios and, in general, much weaker than the expected $M> 10^4\,\text{eV}$
for a correction to the dispersion relation linear in $1/M$. We illustrate this
issue by giving lower bounds on $M$, plus an upper bound coming from
constraints on the size of a quantum ergosphere. We also show that a
phenomenological dispersion relation $\omega^2 = k^2(1+\alpha k^n/M^n)$ is
compatible with observations and, at the same time, has a phenomenologically
viable mass $M>10\,\text{TeV}$ only in the quite restrictive range $0<n<0.68$.
Remarkably, this is the domain of multiscale spacetimes but not of known
quantum-gravity models.
