2015 RX350, with NAV and sub. Not a Mark L system. I am finding differing listings for speaker sizes. In particular I am looking for the size of the mid-range in the front doors, but confirmation of all speakers would be great. Also, does anyone know the approximate output of the OEM amplifier? Thank you.

 

Crutchfield.com would be great for this. Did you try using their site?

 

Yes. They and Sonicelectronics don't even acknowledge the mid-range. They show woofer and tweeter, but no MR.

 

Try some searches here using the term speaker or speakers.
Or just pull off the door panel and take a look.

 

Dash speakers: 3.15”
Front tweeters: 3.15”
​​​​​​​Rear tweeters: 1-3/8”
Front door speakers: 6x9
Rear door speakers: 6.5”
Rear subwoofer: 8”

Edit:
For the door speakers, you will need Toyota adapter brackets to fit regular 6x9s. They also make brackets that let you run a 6.5" in the front doors. The rear doors just need a regular Toyota 6.5" adapter. For the rear subwoofer, it will take a minor amount of fab to get that to fit, but there are some great posts about it. 3.15" Toyota/Lexus speakers can be swapped for an aftermarket 3.5" from JBL or Infinity, etc without modification.