I have electrical problems happened in this order:
intruder alarm starting going off for no reason, has now stopped
smart open thru door handle stopped working, changed battery in remote , hasn’t fixed it
brake lights and headlights stayed on in Auto mode when engine turned off

now finally interior lights and sir con keeps turning on and off continually all the time when engine turned off

so now main issue is smart lock handles and car licking not working

interior lights and air con turning on and off continually when engine OFF

 

Welcome to the forum!

Maybe you can clarify what vehicle you have...there is no 2015 IS200t...I'm assuming it's a 2016 if it's a 200t.

Sounds like you have some major electrical issue inside the car...have you checked for rodents?
I would suspect the issue is somewhere on the driver's side of the dash.
Does the vehicle have any recent history that would be important? Like an accident, recent service, or is a salvage rebuild vehicle.

 

Its a 2015 IS200t

Have taken it back to dealer, they did something to reset everything so it was all working again and then said they tested the battery and it has low voltage and that will be causing the problem.
Anyway, got home and the next day Friday just gone, the initial warning was happening again as soon as I start the engine "restart the system to protect the battery" so I knew it wouldn't be long till all the electric problems started happening again. Low and behold, today can't lock the doors again, air con going on and off when car turned off, the lights and brake lights stay on when car turned off.
I rang the dealer and said as it was within the statutory warranty 3 months from the dealer, then I want the battery replaced free of charge - SUDDENLY their story changed and it has nothing to do with the battery, the test didn't show it being very low at all - well well. Now I have to take it a Lexus Dealer to get a diagnosis done on what is wrong with the car. VERY disappointing seen I only purchased it at the end of November 2020.

 

This is getting confusing...anyway, since you bought it new from dealer, get it fixed under warranty.

 

I think we can just assume it's a 2016 IS200t since Lexus never produced the 200t in 2015...you car may have been built in the later part of 2015, but that still makes it a 2016 model year vehicle...typically the new model is sold around September of the previous calendar year...like my 2014 IS250 was made in August 2013.

Given the randomness of the issues occurring I still think a rodent issue is on the table.
If it's still under warranty, then take it back and let the dealer deal with it.
I've never seen this message before, "restart the system to protect the battery".

 

There is no 2015 is200t. If you bought a car and the documents show “2015 Lexus IS 200t” that is an outright lie, and whoever sold you the car, did not put in correct year of the model.