Yes, Basic is 100% free for up to 15 users.
The only limitation is the number of features you have access to. For example, if you want to use the time clock, payroll integrations, contracts, handbooks, chat, or automatic scheduling, you will have to upgrade to the Pro plan.
When you create a Workfeed account, you get 14 days of free access to all features. This allows you to test the various features before deciding which package you want to continue with.
After the 14 days, you will automatically be transferred to the free version. So you must actively upgrade your plan if you want to continue to have access to the paid features.