Measure the height of your smallest letter (including lowercase). If it’s below 5mm, you may have issues stitching with standard 40-weight thread. You will need to upscale to a 5mm minimum or use a 60-weight thread and thin needle to execute the text reliably. Remember, a 60-weight thread can only stitch satin letters about 25% smaller than 40-weight thread. It can’t perform miracles on overly tiny text.
If small text is too essential and can’t be eliminated, upscale it, even in a limited space. Upscaling can be done by abbreviating words and/or using a tall, narrow font to optimize vertical space. It can also be executed in a simple straight-stitch monoline font at sizes around 3mm. Just remember, if the text is supposed to be read by a viewer, it should be legible from at least 3-4 feet, the average distance between people shaking hands. Consider alternate layouts to allow vital text to be readable.