Skipping Android Security Updates?
You do need to install security updates incrementally, as each release has its own /system image that has had all the previous patches already applied to it. When installing an update, most of the time, /system is completely wiped and then replaced with the new image in your update file.

About the negative performance, a common issue is that the update is dirty flashed, meaning that the /data partition was not wiped with the new system image install. Try first wiping your Dalvik/cache partitions from your recovery. If that doesn't help, you can try wiping /data to see if that will solve your performance issues.

Wiping /data will remove all user data from the device, so be sure to back up any important data before performing a factory reset.