Interchange farming guide

The main advantage of Interchange is electronics stores. Also, the map has a very close extraction point (you should have no backpack to use it). 
When you learn all electronics stores' locations, it will be easy to complete quests like . 
As for keys on Interchange, you will need only

Start learning all stores and places from north to south: TEXHO (most valuable spot at wipe's start), TECHLIGHT (second floor), Rasmussen, German, EMERCOM ( required), TTS and IDEA utility rooms. Check tables, racks, and shelves. In TECHLIGHT sometimes it is hard to spot loot because shelves are high. In EMERCOM room, check the table by the wall and the rack near the table.

Next, follow your way according to your spawn place. If the spawn is far or in the middle, looting TEXHO or Idea utility rooms etc. is useless: it is too late to loot them, or enemies are already nearby. So, we go to the middle of the mall - try to loot Rasmussen, German, EMERCOM, and TTS. If somebody turned on the electricity, you could try looting KIBA (look for AK with a thermal riflescope on the wall). Loot everything that costs more than 8 000 roubles per slot. Wear many-slots chest rig and extract through Hole in the wall EP.

If you aren't confident going inside ULTRA, try to learn and loot Jaeger caches and buried barrels outside.

On the image below, red is the far spawn, and blue is the close one.