Upload & Sell: On
You have 2 options:
1) Upload all your 15 images to an outside server. Then just post the URL links to the description form and they will all show there.
2) Use FM's upload feature and upload the first 4 images to your fist post, then reply to it and add 4 more. If you have 4 pictures for each item, this could be done with 2 replies.