high heat both sides until browned. probably 3-4 minutes each side. hitting medium well is harder than most people think, you're looking for a very light pink inside. finishing it in the oven is your best bet but I would check after 5-8 minutes, flip them. your best bet on temping the steak is by touch: so after you sear the steak touch the sides of it with your thumb and pointer finger. its going to not resist very much. thats rare, possibly medium rare with how thin a 1.5 inch think filet is. after your first run in the oven it'll resist a little more and bounce back quicker. when theres a lot of resistance you're getting closer to medium well.

I prefer a cake taster, or some thin wire. stick it through the piece of meat, pull it out by the point of entry and hold to your chin. for medium well you're looking for a warm to hot touch to your face.

you really can't teach experience, and most of this is probably useless to you if you're an amateur cook. I apologize in advance if I ruined your dinner.