I think it start happened from version 1.4.x, before it took 2-5 min, now it takes 10-15 minutes, the only difference I spotted is that now I have this additional lines:
==> amazon-ebs: Stopping the source instance...
amazon-ebs: Stopping instance
==> amazon-ebs: Waiting for the instance to stop...
==> amazon-ebs: Creating AMI ByPtrpa from instance i-0f3b0382c2dbd1e38
amazon-ebs: AMI: ami-08cae333c0dd917d4
==> amazon-ebs: Waiting for AMI to become ready...
==> amazon-ebs: Copying/Encrypting AMI (ami-08cae333c0dd917d4) to other regions...
amazon-ebs: Copying to: eu-west-1
amazon-ebs: Waiting for all copies to complete...
==> amazon-ebs: Modifying attributes on AMI (ami-05e24b68e270baa51)...
I do not remember such lines prior 1.4 and have not tested yet, but does anyone has same issues or spotted that Packer takes x3 times longer now to create image?