Terrain Lag Issues : Trees

Hello, I am currently making an app for Android. I am trying to make a forest, but with much lag issues when I add trees.

I used T4M on the terrain for it to be mobile-friendly, so it is really smooth without trees.

But with trees it is terrible, with a 1 - 2 fps on my Nexus 7!

I've gotten help from a friend that I shouldn't use any of the standard Unity assets if I'm going for a mobile game. Does anyone know where to point me at for getting mobile-friendly advice, models, and/or textures? Any help would be greatly appreciated.