if you mean that you have given outloook.com the credentials to another email account to retrieve messages via POP3 thus consolidating the messages from both accounts into the outlook.com account the the answer is that the administrators at outlook.com probably only have the server check for new mail every 30 minutes.
To speed things up you might be able to remove the account on the outlook.com side, and then tell the other server to forward inbound mail to the outlook.com account.
If you have one account checking another via POP3, the server doing the checking is only going to be checking on a preset interval, and on a free service such as outlook.com you are most likely not going to have any control over how often that happens. Likewise if the email is being forwarded instead that changes the how often to an event driven, and the event being new email received.
Another way to think about this is the POP3 method is pulling messages over on an interval, while the forward message is pushing based on the event receipt of new mail.