That's a rather difficult question, because it depends on a lot of things. It depends on the device ("2 years old" can be everything from some crappy $60 device up to a Galaxy S5), on the version of Android (because with 5.0, we had this shift in runtimes from Dalvik to ART) on your scene (a high polygon count can be caused by one or two larger objects as well as by many small ones and the performance differs largely between both even if the polygon count is actually the same), on the throttling strategy of the device etc...
As a rule of thumb, larger but few objects are usually faster than more but smaller ones. Rendering lots of polygons isn't as expensive as making lots of draw calls is.
For example, my game Naroth (
https://play.google.com/store/apps/details?id=com.threed.jpct.games.rpg) runs @ around 20fps on most older devices. It renders one terrain with approx. 7000 polygons and many small objects like trees, bushes, gras, enemies, houses, particles etc, which range from 1 to 800 polygons each.
It might help to know, what exactly you want to render.