Crashed game after bringing multiple friendly mobs into small area

After creating a base of operation, I preceded to go and check for horses and donkeys near my base. Upon searching around, I found several horses and continued checking the area. After coming across a N.P.C. village in a Plains, I made a large field into a pasture and started collecting all the horses and donkeys I could find in the area, which totaled somewhere around 70, with more in the area. When I reached around that number the game lagged heavily and crashed several times while I was trying to fly away in creative mode.

Steps to Reproduce:
1. Get into creative mode.
2. Go to a Plains where multiple horses/donkeys spawn in groups of 4 or more in each group, separated by ~20 blocks each.
3. Bring almost every horse and donkey in an area about the size of a medium size N.P.C. village.
4. Try to fly away in creative mode.