Mission: Tip of the Spear
Load Rally Point Alpha and work your way through the mining facility. Upon exiting the final room and procuring a Revenant (or Ghost), you’re almost to the thirteenth data pad. Just drive downhill until you reach a collapsed highway ramp.
See the Warthog, stuck and abandoned in the middle? The data pad is there - climb the nearby pillars and you’ve got it.
Mission: Long Night of Solace
Stop halfway up the stairs to the launching Sabre ship. Turn around. Jump to the platform with the scaffolding and light bulbs.
This part’s a little tricky... you have to get your Spartan to stand on one of the metal bars halfway up the scaffolding, then leap over to the opposite support beam. It might take several attempts for your footing to hold properly. Once you reach the beam, simply run up and grab the fourteenth data pad.
This mission is very difficult on Legendary, so definitely load Rally Point Alpha to save some time. Grab your jetpack from the Bullfrogs, fight through the area where you found Data Pad #6 and, when you’ve emerged back onto the great wide open, turn around and look for the vents pictured below. If you reach the impossible hallway filled with hammer-toting Brutes and Grunt-operated turrets, you’ve gone too far.
Okay, now just follow the step-by-step instructions detailed here. Jetpack to a beam, then up to another beam, then up to a final beam and over to the dark ledge. Now you’re a single well-executed jetpack ride away from reaching the vents and the fifteenth data pad.