First ask the utility, or have the customer do so. For residential condos they probably do not have 'demand' data (typically based on 5 minute or 15 minute intervals), but yiu can ask. If they provide 'Greenbutton' data you may be able to get 60 minute data. See
here for a discussion of using 60 minute data conservatively. There have been a number of discussions on code section 220.87 that debate what you can do with such data if you have it, try doing a search.
Otherwise you'll indeed have to install metering or use another load calc option.