I want to write 15 mm in Creo Sketch.
If I write 15mm, then there is no gap or very little gap between 15 & mm.
If I give 1 space between 15 & mm, then the gap between 15 & mm is too much which is looking odd.
Is there any way to reduce this gap?
I think that the width of space depends on font assigned to text. If you need specific distance between 15 and mm, then you probably has to define two texts instead of one and drive their distance via dimension.
I think you may need to do some trial & error testing with the font type. I set it to win_font and the distance between 15 & mm isn't as bad, when the font is set to default font3d.
You can also do as Martin suggested and create 2 separate text entities and control the distance via a dimension.