Hi,
HikaShop sends the email to the email server of your server/hosting company the second an order is confirmed. If you have a delay, it cannot possibly come from HikaShop. Either your payment gateway doesn't send the payment notification to your server immediately and the orders are only confirmed 45 minutes after the payment (which I doubt), or your email server is not sending the email immediately, or the receiving email server is not processing it immediately.
If you don't have that delay with other emails in Joomla, then the question is different:
What is the difference between the emails sent by HikaShop and the emails sent by Joomla ?
And there are many things which could play a role in the email servers not directly processing the emails.
For example, if you have the PDF invoice plugin enabled and that it attaches a PDF of the invoice to the emails, that could explain why the email server is not processing it directly.
If could be that the other emails you tried are sent in text whereas the emails in HikaShop are sent in HTML. Go in the menu System>Emails, edit the order status notification and turn off the "HTML" setting there so that only the text version is sent and then do a test. If the email is then sent immediately, then you know that it's the issue. Of course, you'll want to keep the emails in HTML or they won't display nicely, so you'll want to check with your system administrator/hosting company what can be done.
If you come from any other setting in the Emails section of the HikaShop configuration (embed images, multiple part, add names, etc) which are all things that the Joomla emails do not do/handle.
So either you do a lot of testing to understand what is slowing down the sending of the emails by the email server, or you contact your hosting company/system administrator to check on with them what's going on, or you use another email server (many services exist for that).