Help! Please with telkom lte

[Jax booster]

Hey everyone i have a b315 router 2-4bars lte signal outside a lte area at home with a lte area being 2-3km away getting 6-9mb/s on a good day which is almost never.

Thinking of getting external antenna
Any advice please or can i change some settings on the router as i have done nothing on the router settings.