Scheduled Apex Batch job taking too long to execute

Question

I have one batch job which delete old account associations then create new account associations & update fields[ For which logic is written in a trigger]

Previously it was taking less time, it executed within seconds, but now it is taking over 2 minutes.

Code

global class AccountAssociationBatchJob implements Database.Batchable<sObject>,Schedulable{    
global Database.QueryLocator start(Database.BatchableContext BC) 
{
    //To fetch the internal type of strategic accounts 
    String Acc = 'SELECT Id,Name,Account_Type__c,Strategic_account__c,AccountNumber,Ext_Cust_Id__c,GPO__c,IDN__c,Strategic__c,National__c FROM Account WHERE Account_Type__c = \'Internal\' AND (Ext_Cust_Id__c LIKE \'NA%\' OR AccountNumber LIKE \'NA%\') AND (GPO__c = true OR IDN__c = true OR Strategic__c = true OR National__c = true)';       
    return Database.getQueryLocator(Acc);

}

global void execute(Database.BatchableContext BC, List<Account> Ac) 
{
    
    Map<String, Id> accountMap = new Map<String, Id>();    
    list<string> Acc = new list<string>();
    Set<string> StrategicAcc = new Set<string>();
    list<string> StrategicAccAssociation = new list<string>(); 
    Set<String> parentAccountId=new Set<String>();
    List<Account> accountsToUpdate=new List<Account>();
     for(Account a: Ac){
        
        if(a.Account_Type__c == 'Internal' && a.Ext_Cust_Id__c != Null && a.AccountNumber != Null && a.Ext_Cust_Id__c.startsWith('NA') && a.AccountNumber.startsWith('NA') ){
            StrategicAcc.add(a.Ext_Cust_Id__c);
        }            
        else if(a.Account_Type__c == 'Internal' && a.Ext_Cust_Id__c == Null && a.AccountNumber != Null && a.AccountNumber.startsWith('NA') ){
            StrategicAcc.add(a.AccountNumber);
        }
        else if(a.Account_Type__c == 'Internal' && a.Ext_Cust_Id__c != Null && a.Ext_Cust_Id__c.startsWith('NA')){
            StrategicAcc.add(a.Ext_Cust_Id__c);
        }
        
        Acc.add(a.Id);
        accountMap.put(a.Ext_Cust_Id__c, a.Id);              
    }
    
    //To get the customer type of accounts where the Strategic_account__c matches with internal strategic account account number       
    List<Account> Acc1 = [SELECT Id,Name,Account_Type__c,Strategic_account__c,AccountNumber,Ext_Cust_Id__c FROM Account WHERE (Account_Type__c = 'Customer' OR Account_Type__c = 'Prospect') AND Strategic_account__c IN : StrategicAcc];        
    List<Account_Associations__c> AccAssociations = [SELECT Id,Account__c,Strategic__c From Account_Associations__c WHERE Strategic__c IN : Acc];
    
    //Delete the existing associtions under all the internal strategic accounts
    if(AccAssociations.size() > 0){
        Delete AccAssociations;
    } 
    
    list<Account_Associations__c> AccountAssociationslist = new list<Account_Associations__c>();
    // Build the association records under internal accounts        
    for(Account a: Acc1){
    
        Account_Associations__c AccAssociationrec1 = new Account_Associations__c();
    if(a.Strategic_account__c != Null && a.Strategic_account__c.startsWith('NA')){
        AccAssociationrec1.Strategic__c = accountMap.get(a.Strategic_account__c);
        //Strategic__C is id of parent A/c, Add the id to list 
        parentAccountId.add(AccAssociationrec1.Strategic__c);  
         }
        AccAssociationrec1.Account__c = a.Id;
        AccAssociationrec1.Account_Role__c = 'Strategic';
        AccountAssociationslist.add(AccAssociationrec1);                     
    }
    if(AccountAssociationslist.size() > 0){
        insert AccountAssociationslist;
    }
    
    //Create a list of Accounts to update
    //After update trigger is fired, Strategic_Account_Owner__c & Strategic_Account_Director__c of child accounts will be updated
    accountsToUpdate=[SELECT Id FROM Account WHERE id IN: parentAccountId ];
    if(accountsToUpdate.size() > 0){
        update accountsToUpdate;
    }
    

}
global void finish(Database.BatchableContext BC) {
    
}

global void execute(SchedulableContext sc)
{
    Database.executebatch(new AccountAssociationBatchJob(),30);
    
}

}