If you have a feeler gauge that is .153 mm., it will be perfectly adequate for a measurement of .150 mm. The error of .003 mm. equates to .0001 inches. The accuracy of the gauge is probably not as close as this.

If you can reliably set the valves to +/- .02 mm., you will be doing just fine.

Please note that you should be setting the valves cold. Cold means letting the engine sit at ambient temperature for 12 hours or more. Don't set them on the same day the vehicle was driven. You would, potentially, be introducing additional error.