Keep it Brief. Time is money in business, so if your voicemail is long, chances are the caller will simply disengage before the cue to leave a message even sounds. Keep your voicemail short. The most should be around 30 seconds, and even that’s pressing it. We’ve grown into a country where our attention span can last only about 10 seconds in some cases, so keep it short, brief and to the point. Persuade and Engage the Caller. If someone calls your business, they already have an intention. It’s the quality of your voicemail that plays a factor if they consider you a company they’d like to deal with. This is your chance to motivate someone to engage in a meaningful conversation with you. If your voicemail is shoddy, chances are they’ll hang up, or lose motivation to continue the call. In other words, your voice mail must engage and entice someone to the point that they care enough to leave you a message.
https://www.indeed.com/career-advice/career-development/professional-voicemail-greeting

If the file you create is too large you can use a tool such as Online Audio Converter to compress the file. This site has a voice recorder option as well.
You may think this is boring, but it’s what works. Leave the sales talk and the promotion for when you call them back. Leaving a greeting is all well and good, but if it has no context you’re going to struggle to stop the person from giving up on you. Make sure people know that they’ve reached the right place. Hello, this is the office of X, the Y department. Please leave your name, reason for calling, and I’ll get back to you as soon as I can. By mentioning the specific department or office they’ve reached, you’re reminding them that they’ve reached the right place, and this is not some generic support department they’ve been redirected to. We talk to lots of different people every day. Make sure you remind people of who you are, and why you’re the best person to handle their call (and more importantly their valuable time). Hello, my name is X, the Senior Manager of Y, I’m sorry I’m unavailable right now, but if you leave your number I’ll return your call as soon as I can. Not only have you revealed who you are, but you’ve also given them the reassurance that their call is important to you. It leaves the right impression. The order of your words can seriously impact how your greeting is received. Research shows that we remember the first and last items on a list best, so the statements that matter most are those at the beginning and those at the end. Hello, you have reached X. I’m out of the office at the moment. Provide me with your contact details and I’ll get back to you as soon as I can. Do you see how important the order of the words is? The name comes first and the call to action is last. Most people will put all this important information in the middle of their greeting. It may not seem like a big difference, but it really matters. It can be tempting to try to fit as much information into a voicemail greeting as possible. Don’t do that. Sometimes less is more. Try to incorporate some strategic pauses into your greeting, so you can let everything sink in. Hello, this is X from Y. [Pause] I am not available to take your call right now. [Pause] If you are calling about Z, then please leave your name and number and I will get back to you as soon as you can.