Nothing wrong with preheat if you have room for the starter sockets.
And if the fixture is capable to hold the heavier ballast.
With F15T8 would be no problem, it is the higher wattage (F20T12, FC8T9,...) what are underdriven on these magnetic preheat ballasts (as it seems all such ballasts are the same, while higher wattage lamps need 0.37A, but lower wattage only ~0.25A).