I have Soft Ground Pro and my left  plant foot just slid right along the ball... WTF? There were 2 long parallel lines left on the ground.(caused by the two back studs dragging along) I had 13 on the back 11 on the front. The sole plate probably has too much earth... Some parts of the field are super soft ans some are quite firm...

The nylon safety studs are longer. They seem to stick to the ground and not release as easily as the aluminium ones. (It sticks to the ground too much I think---slight difficulty in releasing.)
I have yet to try the 13+15 mm combination.

Stud pressure... I didn't feel any, although your foot gets tired after striking too many times or running a lot.