1.8.9 server runs for hours, sometimes days, then lags, then crashes

The server runs for days, or sometimes only hours, and has a maximum of three players. It's hosted in Azure, and we all use windows 10 minecraft PC to access it. After some undetermined amount of time, massive lag happens, then the server shuts down due to watchdog. I increased watchdog to 180 seconds, and it still shuts down. Clearly ticks should not take 3 minutes.