I did this on Legendary, and it was tough, but not ridiculously so. I'd recommend clearing out all the Covenant that you can before you cross the bridge to enter the compound... don't be afraid to use your DMR ammo, the other soldiers will die and leave you some more.
After you clear out all the stragglers, jump back on your Ghost (which you should have at the start of this checkpoint... assuming you grabbed one earlier) and cross the bridge, then maneuver it through the blockades and up the stairs. I used the Ghost from the bridge all the way to the Zealot, blasting every Covenant I could see. Then, when I reached the Zealot, I had plenty of DMR ammo to blast away. Took about 10 headshots, maybe less.
Additionally, you'll find a turret discarded just before the Zealot, you can go back and grab it to clear out the rest of the Grunts. It's kind of a fun level... I imagine it's abusively easy on Normal or lower.