And can you clarify if the 2.5 GB RAM you see is the total RAM that the phone reports, or is it the amount that's being used of 3 GB, or is it the amount that's being reported as free?
Keep in mind that this phone is a low-spec'd budget phone, with a fairly low-performing Mediatek Helio P22 and eMMC 5.1 flash memory (which is significantly slower than higher end UFS 2.1 or 2.2). And 3 GB RAM is really the bare minimum these days for phones -- most mid-rangers have at least 8 GB of RAM.
I don't have any experience with virtual RAM on Android devices, but from what I've seen and read about, it's just a gimmick that really doesn't improve performance. Of course, you're free to pursue this, but I think you'll just be disappointed. Good luck!