Hey,

There are mainly two types of mirror , Concave mirror and Convex mirror. The Concave mirror forms image of different size and at different distance from the mirror. Although convex mirror always form s virtual and diminished image.

Now coming to your question, the Object when placed at 15 cm from the convex mirror and slightly moves towards the pole will keep on become smaller.

Hence the image formed will be virtual and diminished.

Hope that answers your question.

Thank you.