Why is GCE image/instance group performing more slowly than a single instance?

Question

1. I installed wordpress on a single instance. (NGINX, Wordpress & Redis). Then created an instance group for that single instance.
2. I made an image of that instance, then made an instance template. Then created an instance group for that single instance.

Both are using SSD, us-central1-c, n1-standard-1 (1 vCPU, 3.75 GB memory), load balancer, Google Cloud. Essentially, they have the same setup, except for the fact that one is built on a single instance, and the other I made from an image of that instance.

The one made from the image has a TTFB of about .7seconds to 1.2seconds The one made just on the single instance has a TTFB of about .15 seconds to .49 seconds.

Does this mean I am setting up something incorrectly? (also I tried this in two different ways, by installing Wordpress differently both times). Both times it performed more slowly.