How do I only add a value if it’s less than another

I’ve been trying to find a formula that will do this but to no avail. I’m trying to have a table with “breakdowns under 15 minutes” and “breakdowns over 15 minutes” but to do that I need to consolidate all the cells that are below and all above 15 minutes. It needs to be a formula that automatically fills it in based on the future information (because this is for next year). Bonus points if I can do this with only one step.