Server lags even with high fps and lag gets worse as time goes on

I currently have windows 10 and I don't know my specs off hand but I know I have what u would call a low-end gaming pc and I tried to join a server last night that my friend put up just to check out the snapshot together and it started out well but within like 5-10 min. both mine and his game started lagging and he had 4Gigs of ram implemented into the server was barely using any of it and yes he even tried without the extra ram but still the same results and it takes about 2-2.5 to 3 minutes sometimes just to open a chest or door or even a furnace and crafting table I need help on this and if it's something my friend is doing wrong tell me so I can relay the info to him he uses a mac laptop for the server