When you hold a fund (an ETF specifically) you are letting the fund manager do a lot of work for you for usually very low cost (10-20 basis points a year). That

When you hold a fund (an ETF specifically) you are letting the fund manager do a lot of work for you for usually very low cost (10-20 basis points a year). That work is mainly maintaining exposure to the index. A large-cap broad-based ETF will probably hold more names than just the 15 you are holding. The benefits of that are more diversification (potentially lower vol), and regular rebalancing. So crummy names get dropped out and good ones get added in - usually with no tax consequences for you. If you manage your own portfolio of 15 names - you might argue that you could generate tax credits for yourself (tax loss harvesting) which could prove beneficial in certain situations.