In converting my 300L to tubeless last year, I also thought 2.15 on the front would be OTT, but it's fine. As J-Mo said, proper TL rims with the vital sealing bead don't come in the narrow factory widths used by Japanese 250/300 trail bikes. I think Honda choose as thin/light as possible on these bikes for good review performance and low weight figures, but fatter can work better irl.

Be warned though; it's an expensive process which can take months: new rims, hubs (buy from US), lacing and then sealing (which you can DIY) and of course, new TL tyres. I'm not sure I'd bother for domestic day-rides, but for solo overseas travel, it's another matter.
I rushed my DIY sealing, using individual blobs on each spoke (as on many previous TL conversions) but didn't let it cure properly for a day or two, and paid the price. (Tip: avoid puncture sealing fluids like Slime; they may react badly with the spoke sealant and 35°C heat.)
Expecting such problems, I bought some Puraflex 40 sealant with me, and in Marrakech a mechanic did a clean up and re-seal, this time using a continuous band of sealant (not individual blobs). While blobs are better for targeting individual spoke nipple leaks, you also raise the chances of an errant leak by ~36:1 over a continuous band.
As it is, if done well, I've never had a TL spoke leak, nor bent/broken a spoke in decades, but in future will take the continuous band route (like CWC Airtight or Bartubless). If nothing else, it's a lot less time consuming. Probably not needed but adding stretch-free tape round the circumference of the band will resist lifting.

It's true that front flats are a lot rarer, but as I was changing my front to a 19, TL was no added complication and I can leave the levers are home.

I deliberately chose AX41s as close to the stock tyre width, thinking the 300L would do without the extra drag/weight, but though I hate to admit it ;-) fatter rides better on the road, and on the dirt I can't tell at my donkey speeds. Plus as J-Mo also found, a fatter/taller rear on a smaller ø 17 works out same height as original 18er, so speedo reading is back to 8% factory error, and also the gearing drops back down to standard; a nice low 1st.
Below, my link-lowered 300L on fatter-than-stock 17/19 Mitas E07 TLs after wearing out AX41 TLs in 10,000kms. Fat front was all I could buy in Marrakech and felt a bit heavy off the bat, but bike now runs great on the road and fine on the piste for what I do.

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Morocco Overland 4 (2025) • Trans Morocco Trail