Each gun came with two clips each. With the additional 2 clips for the .22 that would be six clips total.
The 9mm clips had a 15 round capacity and the .22 10.
Fully loaded he would have been able to go in there with 72 rounds including one in each chamber.
I read they have found evidence 168 rounds were fired but say it could be as many as 175 to 225 shots fired. That means he had to reload many times after he used up his intial rounds.
Glocks do not feed off of “clips”, they feed off of magazines.
And he had more than four magazines, or so the reports say. They also mention that he was using the 30 or 33 round magazines that are available for purchase.