Unconsciously when we use instagram nonstop, it will drain many internet quota. Whether it's post photo / video or just look at photos on instagram. It turns out everything we do on instagram wastes a lot of quotas, especially.
The best way to save Instagram mobile data is to minimize use when you use mobile data! just like Facebook and Snapchat, there are settings that will make Instagram save data.
Using that way, it's possible that when you see photos and videos take longer to load and instagram does not load preload content again (as usual). If you are scrolling the feed on a mobile connection, you will still burn a fair amount of mobile data; just opening the app will not use much data because Instagram preloads no your feed. In addition, this only works when connected to cellular data.
How to set it is as follows:
Go to Profile-> Options-> Cellular Data Use
 Select Use Less Data
That way your instagram mobile usage is more efficient.