On JD planters it would depend on what frame they are. A JD 7000 conservation planter had two different frames for the four row planter. The narrower one was for 4x30 or 4x38 it would fit in a 15 foot door with the markers locked up. The wider frame which was used on the 4x38 or 6x30 took a full 16 foot to get through with the markers locked up. Slide the marker heads out of the arms will make the planter about a foot narrower.
A JD 1240 4x38 will go in a fifteen foot door. A 1250 will not it is a wider frame.
I do not think any 6x30 planter will go in a 15 foot door unless it is a Kinze turntable planter.