Server lag spikes with processing large amounts of entities in versions 1.9.0 and later. This lag isn't seen in version 1.8.9. It seems the processing of entites results in lag in these later versions. This has been noticed on servers running these later versions lag due to this problem. crash-2016-07-13_05.40.42-client.txt was manually induced in version 1.8.9, notice entites was able to reach 8192 before frame rate dropped below 30.
crash-2016-07-13_05.25.02-client.txt was manually induced in version 1.10.2, entites were able to reach 2048 before frame rate dropped well below 10.

What I expected to happen was...:
No lag until at least 4096 entities

What actually happened was...:
Lag encountered at entity counts much lower than expected. I've noticed a heavy load as low as 1024 entities.

Steps to Reproduce:

1. Place an armour stand using command block command:

   summon ArmorStand ~ ~1 ~ {Marker:1,NoGravity:1,Invisible:1}
   

2. Duplicate armour stand using command block command:

   execute @e[type=ArmorStand] ~ ~ ~ summon ArmorStand ~ ~ ~ {Marker:1,NoGravity:1,Invisible:1}
   

3. using alt+f3 monitor performance while executing first command once, and second command multiple times making note number of entities.
4. Complete this process in minecraft version 1.8.9 and then in later version including 1.10.2