That's a rather steep cut being this close to goal weight, I'm guessing about 120 GW if medium framed.
Also a rather steep cut if mainly desiring fat loss and body improvement at same time.

Should be at 15% max at this point, and that still will be fat loss focus, too steep for body improvement aspect.

When was the last time you took a diet break?

Did you start your cut after a reset? Of how long?

What was your deficit to potential TDEE prior to a reset or starting the 20% cut?

How long did you eat at that level of greater deficit, and how long with no results at the end?

What do you call HIIT, what is the actual routine? (most aren't doing HIIT, just adding more stress to muscle trying to recovery from lifting the day before)

You're 19? You need to be eating more I would say. I'm 5'3 and 140 and 33 years old. When I would try and eat at 1600 my weight did nothing. Friend me if you would like

I'm 19 years old. Heybales, you're right, I do want to end up at 120 as my GW, or 20% bf. So I'll decrease my cut to 15% as both of you have suggested. I took a diet break from febuary to may, where I was eating at TDEE uninentionally more or less. After that, I decreased my calories to 1400, found that too hard to maintain, whilst my weight didn't budge. Upon discovering EMTWL, I upped my calories to 1600, however I do end up netting around 1700-1800 weekly by looking at my graph app.

For HIIT, I run for 20-25 min twice a week, alternating between all-out sprints and recovery periods of walking. That in itself is so exhausting and challenging, that I'm surprised that I haven't seen any improvements till now. I am red in the face and gasping by the end.

Good job on reset, I think you just need less deficit at this point and with that routine to see positive results.

So with lifting 3 x weekly for max body recomp, there is no where you could safely fit in that attempted HIIT routine without negatively impacting the lifting.

Just for you to see and be convinced, you'll need a way to see either your HR or your pace during the sprints. Because comparing the feeling that you are wiped out isn't useful, it'll feel the same either way.
So for one time on your lifting workout after your rest day, skip the lower body lifting, and after the upper lifting, go and do the HIIT routine.
If you have a HRM you'll likely notice how much higher you can push your HR on fresh legs rather than tired and recovering legs.
If you have a means of seeing speed, you'll be faster. Or perhaps if you do the sprint until you feel like you can't anymore, that should be seen to be longer.

And without some form of objective measurements, you'll never know if it's improving. The state you end up in is what you should end up in, burning legs and out of breath. The problem comes from the fact it pretty much feels the same with either tired legs or fresh legs, until you can really compare the difference.
I just did hill sprints last night after upper lifting only routine. And despite hitting sub-5 min/mile pace during the sprint up, my HR actually never went in to anaerobic HR zone. That's because of tired legs from 2hr hard bike ride on Sun, not fully recovered. So I felt strong just going by feeling, but obviously wasn't. That's the difference.

But if you are doing the lifting properly, and with your desired changes, you should, the day after lifting should be rest, to allow for best recovery and repair stronger from the lifting.

Exercise tears down, it's the rest that actually allows recovery and repair to build back up stronger.

HIIT in fact started out as the recommendation for those that ONLY wanted to do cardio, perhaps an event or something, to give them something lifting-like with same response. All-out anaerobic push with brief recovery, repeat. The response by the body is the same as lifting if done correctly, increase strength and build more muscle if nutrition allows.

But would you lift with the same muscles day after day? Same thing here, no, because you won't get the best of either workout really, the lifting never gets full recovery, the HIIT isn't really and doesn't get expected response.

If lifting heavy, skip the HIIT. You can attempt intervals right after the lifting if desired, just for the effect of burning more in shorter period of time. This should make it very obvious the difference between tired and fresh legs.
But day after cardio to allow recovery to the lifting, should be the Active Recovery HR zone, called such because it is expected to add no further load to the muscles, just increase blood flow and aid repair. It has been poorly called by the fad name in recent years "fat-burning zone".

Now if you want some running specific improvements, skip lower body lifting 1 session a week or every other week, and do that HIIT instead. Same response, needs same recovery.
And then that Recovery HR zone running will train the aerobic fat-burning system, which you actually need too.
Train the high and low end.

Wow guys, thanks so much for all your replies! I was currently working with ten pound dumbbells, which are now seeming too light, so I shall be getting 15 pound dumb bells by next week. Heybales, thanks for your detailed response. Do you mean to say that after my rest day on Sunday, I should just train my upper body and do HIIT on Monday, then gap (rest) on Tuesday, then train lower body on Wednesday, then rest on Thursday, and HIIT etc again and so on? Just want to make a clear cut timetable and follow what you've told me!

I threw an option in if you are doing the HIIT because your goal is some cardio event, like half-marathon or such.
In which case the HIIT would be useful to strengthen running specific muscles.

If not, then skip the HIIT, just slow jog on day after in fat-burning zone.