2015 exl has the halogen reflector headlight which is not very good. It's a big downgrade from the projector headlight of 2017 IMO. If I had projectors, I would upgrade with LEDs or HIDs kits. My 2013 Venza oem HID headlight blows it out if the water.
2015 doesn't have blind spot monitor, lane assist, signal mirrors, adaptive cruse control, garage opener.

 

I have a 2015 EXL (AWD, 2.4 NA), wife has 2019 EXL (AWD, turbo 1.5, which is somewhat similar to the '17). I drive them both, but mostly my '15.
My '15 (at 68K):
No major issues, although it does have the "automatic door unlock issue" (not sure what's going on, but it does seem to cause a parasitic drain on the battery).
Goes through rear pads and rotors every 30k. Last time I took pads out after 15K and cleaned/ lubed, still only got 30K Still on original fronts. My driving habits would be considered gentle.
I find that the halogen headlights are more than adequate.
I don't miss the driving "aids" when in my '15, other than the adaptive cruise control when on trips.
I don't use the phone features in my '15 (other than bluetooth phonecalls).
Radio is better in the '19.
'15 has a CD input (which I rarely use). All my music is stored on a 128 GB USB.
The '15 has more road noise than the '19, but not that objectionable.
The turbo 1.5 engine/ CVT transmission in wife's '19 seem much more refined- the '15 2.4 NA engine revs higher in light load situations (probably to be expected with the higher torque at low rpm with the turbo 1.5). Engine on the '15 revs over 4K on some uphill highway grades at 65-75 MPH. The '19 does not rev that high in the same conditions.
I've been averaging 29.5 MPG (calculated) since new on my '15. That includes four months of snow tires and year-round Thule square bar roof rack). My highway mileage goes down to 26 when carrying one kayak Wife's '19 has averaged about 31.5 (indicated) since new (no snow tires or roof racks).
Good luck.

 

Nothing wrong with the 2015 for the kids to run around in. It will last a long time.
But one thing that hasn't been mentioned is safety technology.

 

Yeah, when I looked up the old 2015 brochure today, many of the things that came standard with my 2017 EXL were only in the Touring level of the 2015 (safety systems, power lift gate, dual seat memory).

 

Darn it, another dealer is giving him more for the trade so it'll cost me $14K now. Still a fair value I think. Just need to decide if I want to get it for maybe 2-3 years use despite it missing a number of the tech, convenience, and safety features compared to our 2017 EX-L.

 

Plead with your brother to give you a deal!