10W-30 oil is a lighter or thinner oil than 15W-40 I believe.
Be careful cause most 10W-30 is for gas motors and not Diesels, although there is apparently a
Diesel version.
If it were mine, I believe I’d stick with the 15W-40, being a turbo
motor it’s my belief that a multi vis oil is called for.
I would also be very tempted to re-route my crankcase vent to a catch can myself, I think
plumbing one into the suck side of the turbo to be foolish, but understand it’s likely done to pass emissions.
It does funk things up, and add even a tiny amount fo dust, say belt dust and it’s a mess, you really ought to do the wash like Yanmar says.
Or don’t feed the turbo oil mist