I heard that one of the extra costs/risks of buying a ETF compared to a normal index fund/mutual fund is the sell and buy spread.
And I heard the extra costs/risks of buying a mutual fund compared to a ETF is the sell and buy fees ;)
Each day your ETF or index fund will change in its price more then the spread is. Its likely that the difference between cheapest/most expensive stock exchange at a certain time point is higher then this difference at least once a day.
"0,15% higher annual cost per year"
That says it, doesnt it?
Divide the spread with the 0,15% and you have your answer: If you hold the ETF longer then 2 years, the spread costs you less then the fund (all other things equal).
But again: The time you buy on a given day is more important then the spread in most cases.
So if you buy automatically for 10 years, you can ignore virtually any spread. If the spread is more then one percent you probably shouldnt choose to buy it for 10 years anyway, because that ETF is too small or specialized.