Look at the starting material.....This is a tertiary halide with an excellent leaving group. Tertiary halides LOVE to do the E2 reaction, especially when strong nucleophiles such as methoxide, ethoxide, amide, or hydroxide are employed. Here....you are using methoxide on a tertiary halide, thus E2 would indeed be the major product. I would say 85% E2 with 15% Sn2 minor,,,,and I am being generous towards Sn2.
I hope this helps.
Dr Romano