ODE15i is variable-step and variable-order, so "the" step size and "the" order used would each be sequences as long as the number of steps. You can supply an output function to be called after each time step. It could store the previous step's t value as a persistent and calculate the step size. Or you can make the TSPAN a two-element vector (in which case the first output t will be the t-values at each time step, so the step size diff(t)). Off-hand I can't think how to get at the sequence of orders used.