It is latency, nothing else. And Nest gets ticks for all the scripts of bse, nse, cds, mcx simultaneously whether a given client likes it or not. For example, I trade only 2 instruments. Don't even look at others. Yet I know my terminal is getting all the ticks of all the instruments, even though I have permanently ticked off BSE BFO, NSE downloading during startup (which incidently made the starting up damn fast).
If somehow there were an option in preferences that would make the terminal more 'intelligent' as to serve only the data for the instruments on the watchlist, I think this data bottlenecking at clientside will vanish. However, it is a big IF - judging by the hotch potch job omnesys guys have consistently been doing in bringing out this and that version of shoddy Nest or Pi in the sky.