R,
you can check interferences and coverage. That’s all you can do at radio level.
Most probably, you need to increase your radio and abis capacities.
Perform drive tests to see why your EDGE throughput is so low…
regarding the RTT, that seems like a good value.. what RTT of subsequent pings ? (meaning, pings coming AFTER the first ping : the first ping takes a while usually.. the next pings are faster because they reuse the same TBF)