GENERAL_READ_ENTITY_START: The more request means slower read from cached objects?

Please do not judgme for the type of question. It might be about software algorithms and concepts. That is why I must write the link that it is already asked on server fault.

1- > the algorithm and concept of project .net web app.

Client's onblur event makes an ajax call-> UI -> functionUI() -> > APP <<

functionUI()

int limit=450;
public bool functionUI(){

for(int i=0;i< limit ; i++){
functionApp(i);
}

}


public static bool functionApp(int i){
foreach(HolidayEntity h in Global.holidayGlobals.Values /*CachedList*/){
if(h.Value == i){
return false;
}
return true;
}

}
2- The question The limit value from ui side if it is 2 or 20 times the response duration is good . But when it is 450 times. It takes 40 seconds to get a result in client side. I know the code is not well organised but the question is why the application side so slow when it is responsible to make more calculations.

Any clue will be so usefull. Thank you.

Servers are Server 2018 SP 1, .net Frame Work 4.0.30319.42000 It is only happened in production environment. In development side the application runs quite fast even the limit is 450.

GENERAL_READ_ENTITY_START and GENERAL_READ_ENTITY_END 57 ms.. so how to fix it ? Why this part could be slow ?