Since nobody answered about the 15w50 in your engine, I'd say it's probably not going to hurt anything but your gas mileage. It's summer and it doesn't appear that the 6VE1 has super tight clearances on oil ports, so you'll just be running extra high oil pressure when the oil is cold.
For the oil consumption, check out the following thread and draw your own conclusions. Mine doesn't even burn, but I'm switching anyways due to prior experience with 15w40 oil in other engines.
http://forum.planetisuzoo.com/viewtopic.php?t=7033
The Mobil-1 5w30 Truck & SUV oil seems to be popular here, and can be purchased cheaply at Wally World if you prefer to stay within manufacturer's specs.