Very happy to see another unreal entry! Very good graphics I appreciate that. Also the main menu buttons were awesome I am curious how were they done.
But there are many things you can improve.
1. The music is good but it doesn't really fit the vibe of the game.
2. The gameplay was very simple and I honestly didn't really find the theme there.
3. The size of the game is huge. In Project Settings->Packaging there is an option 'compress cooked packages' who would like to tick that. Also, another option 'cook only maps', and 'exclude editor content' must be ticked. For a detailed tutorial watch this tutorial by matt aspland Packaging And Exporting Your Game - Unreal Engine 4 Tutorial - YouTube
4. Countdown of the 15 seconds is a bit too much for every time I play. So, I would suggest to keep the waiting time 15 seconds for the first time a player plays, but for the next time, only 5 seconds. And also it should update the time every second. I saw it was fixed at 15.
But since this was your first game jam, I highly appreciate what you did! Good job and well done.