Server has low TPS and crashed

When there are no players on the server, the TPS is kept at the level of 5-11 (normal 20). When several people come to the server, it crashes and falls. The console makes a mistakes: "Server thread/WARN Can't keep up! Is the server overloaded? Running 13387ms or 267 ticks behind" and "Large Chunk Detected: ([4, -3]) Size: 2,835 ./world/region/r.0.-1.mca".