def get_top_15_marketcap(data):
    """
    Gets the top 15 companies based on their marketcap.
    Parameters:
        (list)data: A compiled list of lists of company data.
    """
    top_15_marketcap = list()
    all_company_marketcap = list()
    for line in data:
        company_tag = line[0]
        company_marketcap = line[3]
        all_company_marketcap.append([company_marketcap, company_tag])
    all_company_marketcap.sort(reverse=True)
    for i in range(0,15):
        top_15_marketcap.append(all_company_marketcap[i])
    return top_15_marketcap