I wouldn't worry about it and use what ever you want, seriously.
When have you ever heard or not only an oil related engine failure, much less a viscosity related failure.
I have vehicles and toys with various viscosity and or synthetic oil requirements of all kinds.
I think my total cylinder count is around 60 right now from powersaws and mowers, boat, car, trucks, old and new.
EVERYTHING gets 15W-40 (I'll lower that here in AK this winter in the trucks) diesel rated oil. Buy it on sale multiple cases at a time. Hasn't been a problem for lotsa years.