Your device have QHD resolution display. It is a great stress for much more serious graphic cards, and even more for tablet.
On specialized devices with much lower resolution present is a large slowing in use when you are included DEM files.
No optimization there can not help, only stronger graphics card, or stronger device.
I know that in the android there are some adjustability thus effectively weakening the quality of the picture, renders a smaller number of pixels...but it has nothing to do with navigation program.