I recently installed an extender (E3200). This, of course, improved the wifi signal in areas of the house far from the router (G3100). However, the latency is worse in some areas. For example, there is this couch in between the router and the extender where I often sit that increased its latency from 7ms to 14ms (based on speedtest.net).
It's worth noting the router and the extender are connected via a coaxial. The coaxial network was already in the house before I moved in. I noticed there's this splitter in between the router and the extender (I'm not sure if there are more).
Any recommendations on how to improve latency?
Just +7ms? It is within the technicality.
If you have more nodes (Internet -> G3100 -> E3200) in your network, your latency will increase in general.
You can try uplink E3200 with ethernet to G3100, but I don't think you have existing wiring.