Part# for Toyota Sienta 1.5L hybrid 2015

Your local NAPA, Advanced, Carquest or O'Reilly auto parts store should be able to determine those part numbers from several manufacturers or plugs.

When I went to Bosch's website to look up that car for Iridium Spark plugs, it does not show that car as an option.

https://www.boschautoparts.com/en/auto/spark-plugs/iridium-spark-plugs

Scroll to the bottom to enter car information.  If you have the VIN, you can get direct info, otherwise it is by year, make and  model.

Are you sure this car is meant to use Iridium Spark Plugs?

That said, have a look at this site, it lists your vehicle, but I do not know which model: http://ngk-sparkplugs.com/toyota-sienta-c-180_2051_3648.html

Edit: (Oh, I see this is not a US vehicle. That explains the problem.)

And is this your part? https://www.megazip.net/zapchasti-dlya-avtomobilej/toyota/sienta-38368/ncp175-55309/ncp175g-mrxnk-912847/ignition-coil-spark-plug-17765433#/il-411857704-3868694-3868694

Thanks Owen;  right, my car is not used in the US.
It's parallel import direct from Japan & the manual that comes
with it is completely in Japanese which I don't understand.

Based on the link you posted above,
  it's  TOYOTA ::  SIENTA ::  NCP81G 2WD
though from the Wikipedia link above,
  it's 1.5L 1NZ-FXE I4 hybrid  Year 2015


Saw your megazip link but I still have doubt.  So is the part in
the megazip link referring to one of the parts in the 2 links below?:

https://www.ebay.com/itm/4x-Iridium-Spark-Plug-90919-01240-SK16R11-Fit-Toyota-Corolla-Matrix-Scion-Prius/142845005345?hash=item214239ce21:g:3G4AAOSwIJtbhQcQ 

https://www.ebay.com/itm/4-x-Denso-SK16R11-Iridium-Spark-Plug-For-Toyota-Corolla-Matrix-Prius-90919-01240/302484239583?_trkparms=aid%3D555018%26algo%3DPL.SIM%26ao%3D2%26asc%3D52885%26meid%3D2a7926a43c9c44a4b408d97eaa01f0b2%26pid%3D100005%26rk%3D3%26rkt%3D12%26mehot%3Dag%26sd%3D142845005345%26itm%3D302484239583&_trksid=p2047675.c100005.m1851

or this one?
  https://www.ebay.com/itm/6pcs-Iridium-Spark-Plug-Set-of-Genuine-for-Toyota-Lexus-90919-01247-FK20HR11/292413391414?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2763.l2649

So looks like the part# SK16R11 & SK16HR11  are not the same (with the extra "H") ?
The eBay item for the item with the extra "H" is about double the price of the item
without "H"

The one I found had the H.  I tried to find the main difference but the data on these parts is fairly slim.