Macbook Pro 2015 waking from sleep every few seconds
I had a similar issue with my 2015 Macbook pro 13. Even if I had turned off tcpkeepalive and power nap, the system was waking up from sleep. In one of my tests I realized that if I close the lid and enter sleep while the charger was plugged in, the system wakes up from sleep, because "Power Adapter" settings are left effective. Eventually, I had to turn off "Wake for Wi-Fi network access" and powernap for both Battery and the Power Adapter modes. 

Just to test if this is the issue, can you try to first unplug the laptop from charge, and then close the lid to enter sleep, and see what happens?