I have a data structure with 15 unsigned longs, I have defined a hash function using hash_combine as follows:

 friend std::size_t hash_value(const TUPLE15& given)
    {
      std::size_t seed = 0;

      boost::hash_combine(seed, val1);
      boost::hash_combine(seed, val2);
      ...
      return seed;
    }

I insert a large number of values into a boost::unordered_map but the performance is not good enough. Probably, I could do better with an alternative hashing function. To confirm this, I need to check how many collisions I am getting. How do I do this?