Minecraft crashing in Realms and other peoples worlds

So every time i'm in someone else's realm i crash after playing for 15 minutes. Also when i'm in a someone else's server i end up crashing after only being there for 5 minutes. The only reason i know i'm crashing is because my internet is good and my computer can run minecraft perfectly. I just think its the new update that wont let me play like i used too.