At this age, appetite is varied and this is absolutely normal. Don't force feed the child. Just make it 5 to 6 meals per day. Change the meals every time you give. Like egg, kichdi...
Coming to sleep pattern 15 months old child sleeping at 2am is not a good sign. Cut off the digital screening. Feed early, around 6pm in the evening. Put him/her to sleep by 8pm. It may take some time in the beginning, gradually the kid adjusts.
Next Steps
Strict change the sleep pattern
Health Tips
Cut off the screen time.