  Influence of the plasma collisions on the laser-driven collisionless shock
formation and subsequent ion acceleration is studied on the basis of two
different collisional algorithms and their implementations in two well-known
particle-in-cell codes EPOCH and SMILEI. In this setup, an ultra-intense
incident laser pulse generates hot-electrons in a thick target, launching an
electrostatic shock at the laser-plasma interface while also pushing the
interface through the hole-boring effect. We observe, to varying degrees, the
weakening of the space-charge effects due to collisions and improvements ($\ge
10\%$) in the energy spectra of quasi-monoenergetic ions in both PIC codes
EPOCH and SMILEI. These results establish the `collisionlessness' of the
collisionless shocks in laboratory astrophysics experiments.
