Generate 15 random numbers that may be the same 2 times but not 3 times

I am working on a scratch card in PHP and i need to build the backbone behind it.

My plan is as following: 1. Generate 15 random numbers ( there are 8 containers and 15 images to choose from. ). 2. Each number correspondences with a image ( 1 is image 1, 2 is image 2 etc. ). 3. Show a random image (1/15) on container 1, show random image (1/15) on container 2 etc. There are 8 containers to be filled.

What i currently can't figure out is to check if there are duplicate numbers, and if so it is fine to have 2 duplicates but not 3 since that would mean a win.

What i have now is this:

$images = array();
for ($i = 0; $i < 8; $i++) {
    $random[$i] = rand(1,15);
}

This will fill $random with 15 numbers i can use. Now i want to check if within those 15 there are duplicates. But the trick is that duplicates are no problem ( and even preferred on some degree ) but once there are 3 of the same numbers i want one of those to change again in a random number ( and re-check for duplicates).

So what should be fine ( 2x 8 is fine, 2x 1 is fine ):

Container 1: 14
Container 2: 8
Container 3: 8
Container 4: 4
Container 5: 1
Container 6: 9
Container 7: 1
Container 8: 12

What should be incorrect ( 3x 14 is not fine ):

Container 1: 14
Container 2: 8
Container 3: 4
Container 4: 14
Container 5: 14
Container 6: 9
Container 7: 1
Container 8: 12

You guys have any advice on what the right way is here? I am trying to stay away from a lot of "if's".