We are experiencing a similar issue.
Currently, our app’s loading time on iOS (iPad Air) is 6 sec but on new Android (Galaxy Tab S) it is 40 sec, which is unacceptably long. After doing some research we’ve discovered that the initial file system read operation done by Vuforia becomes extremely slow. Each such read operation takes ~15 seconds (!).
Really interested to know how you tested this.
I seem to have encountered the same problem, with loading times exceeding 30 seconds and up to 80-90 seconds on a Samsung 3 and HTC One M7 Android device.
I am also using Unity3d 4.5.4 and Vuforia 3.09.
At first I though that this problem was due to the number of markers I have in the scene.
During testing I kept all the markers enabled, but had 2 versions of the app. The difference between these 2 version was the size of the Resources folder (No difference in code or loading assets from the resource folder).
The bigger\more items in the resources folder I had, the longer it took for the scene to load/initialize.
As this behaviour only occures in the scene which is included Vuforia components such as the AR camera/Image targets, I suspect that this problem has something to do with Vuforia (It might be testing something in the resource folder?)
I still need to test to see if there any differences in the loading time realted the size of the Resource folder in IOS.
Any further insights into this problem would be appreciated.