Is 150 degrees in my oven equal to high in a slow cooker?

Agree with francophile on this. I use a Le Creuset cast iron pot to slow cook in the oven. Bolognese sauce goes all day at 200 degrees, a roast will go for 6 hours at 220, unless it's wild game and then I would cook it longer and slower.

It depends on what you're cooking and vessel within which you are cooking. Is it a glass or ceramic bowl? To use your oven like a slow-cooker I.e., long term all day braising, a 220 degree mark is good for dishes containing proteins. Vegetable based dishes would need no more than 150 degrees

No it is not. To braise in an oven you would need it to be 325 to 350 degrees. http://blog.williams-sonoma.com/slow-cooker-vs-dutch-oven-a-conversion-guide/

Oven is dry indirect heat so that would matter on what your using it for. But no I would think a slow cooker should have settings up to 200 degrees F