Ok, the first trouble code B1634 is a body error telling the right mirror adjustment motor is bad, not a brake code. A brake code would be a C code. The C1015:64 is a vacuum supply problem. Faulty vacuum sensor or vacuum pump. I would think replacing the sensor, not the booster would be the solution.
Error codes are a guide in a diagnostic troubleshooting process, NOT, a “replace this part” instruction. So, no, the dealer has not found the core problem(s). I think you should have the service writer, or the service manager explain why you paid $3000 for a mirror code and why they think swapping the booster will fix a sensor problem. The answer or lack of one will determine if you should change dealers.
I suspect they are guessing and changing parts rather than actually diagnosing the problem(s). The flip side is a hybrid is a complicated car that is expensive to repair.