Commercially produced plants are usually grown immersed rather than submerged. They are therefore not used to being underwater and need some time to acclimate. Its possible you could lose all original growth to melt, but new growth should be healthy. From your other post, your tank has been going a little over a week. That isn't long enough to decide whether your plants are doing ok or not.
I had to look up your light, its a pretty standard domestic type lamp? You're correct that all your plants are low light requiring. Looking at the specs for that lamp on B+Q website, the light output based on 10 to 20 lumens per litre for low light demanding plants would be sufficient for a 50 litre tank depending on how far the light source is from the tank. Your tank is 14 gallons (50ish litres) so that works ok. I would have concerns about the 2700 kelvin colour temperature of the lamp. 5500 to 6500 kelvin would be better. Your plants will probably be ok with that lamp, but would benefit from an aquarium light.
I would see how things go, if you get good new growth, then great. If things dont improve, get a lamp with 500 lumens output, and a colour temperature of 5500 to 6500 kelvin. Most aquarium lights rated for your tank size will meet this if you cant find the specs.
Also, you wont necessarily get good results from all your plant types. Grow the plants that thrive, remove the plants that dont.
