Here are some stats on scaling up images from the low-res cache. Images, in this case, are photos taken with the device.

Nexus 6: 3-4 ms (running Android 6.0, Chrome version 60.0).
Nexus 4: 0-1 ms (running Android 4.4.4, Chrome version 60.0).

Nexus 4 has smaller images and scales up to a smaller size.