<?php
$arr = [
0 => 1,
1 => 2,
2 => 1,
3 => 2,
4 => 8,
5 => 7,
6 => 6,
7 => 6,
8 => 6,
9 => 5,
10 => 8,
11 => 4,
12 => 1,
13 => 1,
14 => 1,
15 => 1
];
$res = array_slice( // get first 5 values
array_unique( // get only unique values
array_reverse($arr) //reverse array for get last values
)
,0,5);
print_r($res);